Display device having shared column lines

ABSTRACT

A display device having at least a plurality of pixel circuits, connected to signal lines to which data signals in accordance with luminance information are supplied, arranged in a matrix, wherein pixel circuits of odd number columns and even number columns adjacent sandwiching an axis in a column direction parallel to an arrangement direction of the signal lines have a mirror type circuit arrangement symmetric about the axis of the column direction, and there are lines different from the signal lines between signal lines of adjacent pixel circuits.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.15/282,075, filed Sep. 30, 2016, which is a Continuation Application ofU.S. patent application Ser. No. 14/932,620, filed Nov. 4, 2015, nowU.S. Pat. No. 9,460,669 issued on Oct. 4, 2016, which is a ContinuationApplication of U.S. patent application Ser. No. 14/627,045, filed Feb.20, 2015, now U.S. Pat. No. 9,202,424 issued on Dec. 1, 2015, which is aContinuation Application of U.S. patent application Ser. No. 14/452,771,filed Aug. 6, 2014, now U.S. Pat. No. 8,988,327, issued on Mar. 24,2015, which is a Continuation Application of U.S. patent applicationSer. No. 13/768,349 filed Feb. 15, 2013, now U.S. Pat. No. 8,937,581,issued on Jan. 20, 2015, which is a Divisional Application of U.S.patent application Ser. No. 12/923,635 filed Sep. 30, 2010, now U.S.Pat. No. 8,519,915, issued on Aug. 27, 2013, which is a DivisionalApplication of U.S. patent application Ser. No. 11/137,657 filed May 26,2005, now U.S. Pat. No. 8,378,930, issued on Feb. 19, 2013, which claimspriority from Japanese Patent Application No.2004-159378 andNo.2004-159379 both filed in the Japan Patent Office on May 28, 2004,the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pixel circuit having an electroopticelement controlled in luminance by a signal line in an organicelectroluminescence (EL) display device, liquid crystal display (LCD)device, or other active matrix display device and an interconnectstructure and arrangement and circuit in an image display device inwhich these pixel circuits are arranged in a matrix.

2. Description of the Related Art

In an active matrix type display device, use is made of electroopticelements such as liquid crystal cells and organic EL elements as displayelements of pixels. Among them, an organic EL element has the structureof a layer made of an organic material, that is, an organic layer,sandwiched by electrodes. In this organic EL element, by applying avoltage to the element, electrons are injected from a cathode into theorganic layer, holes are injected from an anode into the organic layer,electrons and holes are re-coupled as a result of this, and therebylight is emitted. This organic EL element has the followingcharacteristics:

(1) A luminance of several hundreds to several tens of thousands ofcd/m² is obtained by a low voltage drive of 10V or less, so it ispossible to lower the power consumption.

(2) Being a self light emitting element, a contrast of the image is highand a response speed is fast, so the viewability is good, making thissuitable for display of moving pictures.

(3) Being a completely solid element having a simple structure, it ispossible to raise the reliability of the element and reduce thethickness.

An organic EL display device (hereinafter, described as an “organic ELdisplay”) using organic EL elements having these characteristics as thedisplay elements of pixels is considered promising for next generationflat panel displays.

As the methods for driving an organic EL display, there can be mentionedthe simple matrix method and active matrix method. Between thesemethods, the active matrix method has the following characteristics:

(1) The active matrix method is able to hold the light emission of theorganic EL element at each pixel over a one frame period, so is suitablefor raising the definition and raising the luminance of an organic ELdisplay.

(2) The method enables preparation of peripheral circuits using thinfilm transistors on a substrate (panel), so enables simplification ofthe interface with the outside of the panel and raises the functions ofthe panel.

In an active matrix type organic EL display, generally use is made ofpolysilicon thin film transistors (TFTs) using polysilicon as the activelayer for the transistors used as the active elements. The reason forthis is that a polysilicon TFT has a high drivability and enables designof a small pixel size, so is advantageous for raising the definition.

While polysilicon TFTs have the characteristics explained above, it iswidely known that they suffer from a large variation of characteristics.Accordingly, when polysilicon TFTs are used, suppression of thevariation in characteristics and compensation for the variation ofcharacteristics of TFTs circuit wise are major issues in active matrixtype organic EL displays using the polysilicon TFTs. This is due to thefollowing reasons.

Namely, this is because while a liquid crystal display using liquidcrystal cells as the display elements of the pixels is configured tocontrol the luminance data of the pixels by voltage values, an organicEL display is configured to control the luminance data of the pixels bycurrent values.

Here, an active matrix type organic EL display will be explained inbrief. FIG. 1 is a diagram of a general active matrix type organic ELdisplay, while FIG. 2 is a circuit diagram of an example of theconfiguration of a pixel circuit of the active matrix type organic ELdisplay (refer to for example U.S. Pat. No. 5,684,365 and JapaneseUnexamined Patent Publication (Kokai) No. 8-234683).

In an active matrix type organic EL display 1, m×n pixel circuits 10 arearranged in a matrix, n number of columns' worth of signal lines SGL1 toSGLn driven by a data driver (DRV) 2 are arranged for each pixel columnof the matrix array of these pixel circuits 10, and m number of rows'worth of scanning lines SCNL1 to SCNLm driven by a scan driver (SDRV) 3are arranged for each pixel row.

Further, the pixel circuit 10 has, as shown in FIG. 2, a p-channel TFT11, a n-channel TFT 12, a capacitor C11, and a light emitting element 13made of an organic EL element. In the TFT 11 of each pixel circuit 10, asource is connected to a power supply potential line VCCL, and a gate isconnected to a drain of the TFT 12. In the organic EL element 13, ananode is connected to the drain of the TFT 11, and a cathode isconnected to a reference potential, for example, a ground potential GND.In the TFTs 12 of the pixel circuits 10, sources are connected to signallines SGL1 to SGLn of corresponding columns, and gates are connected tothe scanning lines SCNL1 to SCNLm of corresponding rows. One end of thecapacitor C11 is connected to the power supply potential line VCCL, andthe other end thereof is connected to the drain of the TFT 12.

Note that the organic EL element has a rectifying property in manycases, so is sometimes called an organic light emitting diode (OLED).Use is made of the symbol of a diode for the light emitting element inFIG. 2 and other figures, but a rectification property is not alwaysrequired for the organic EL element in the following explanation.

In a pixel circuit 10 having such a configuration, at a pixel forwriting luminance data, the pixel row including that pixel is selectedby the scan driver 3 via the scanning line SCNL so that the TFTs 12 ofthe pixels of that row turn ON. At this time, the luminance data issupplied from the data driver 2 via the signal line SGL in the form ofvoltage and written into the capacitor C11 for holding the data voltagethrough the TFT 12. The luminance data written in the capacitor C11 isheld over a one field period. This held data voltage is applied to thegate of the TFT 11. By this, the TFT 11 drives the organic EL element 13by the current according to the held data. At this time, gradations ofthe organic EL element 13 are expressed by modulating the voltage Vdata(<0) between the gate and source of the TFT 11 held by the capacitorC11.

In general, the luminance Loled of an organic EL element is proportionalto the current Ioled flowing through the element. Accordingly, thefollowing equation (1) stands between the luminance Loled and thecurrent Ioled of the organic EL element 13:

Loled∝Ioled=k(Vdata−Vth)²   (1)

In Equation (1), k=1/2·μ·Cox·W/L. Here, μ is the mobility of thecarriers of the TFT 11, Cox is a gate capacitance per unit area, W is agate width of the TFT 11, and L is a gate length of the TFT 11.Accordingly, it is seen that variations of the mobility μ and thethreshold voltage Vth (<0) of the TFT 11 exert an influence upon thevariation of luminance of the organic EL element 13.

In this case, even for example when writing the same potential Vdata todifferent pixels, since the threshold value Vth of the TFT 11 variesaccording to the pixel, the current Ioled flowing through the lightemitting element (OLED) 13 varies by a large extent and consequentlybecomes completely off from the desired value, so it is difficult toexpect a high image quality of the display.

A large number of pixel circuits have been proposed in order toalleviate this problem. A representative example is shown in FIG. 3.(See for example U.S. Pat. No. 6,229,506 and FIG. 3 of JapaneseUnexamined Patent Publication (Kohyo) No. 2002-514320.)

A pixel circuit 20 of FIG. 3 has a p-channel TFT 21, n-channel TFTs 22to 24, capacitors C21 and C22, and an organic EL element 25 as a lightemitting element. Further, in FIG. 3, SGL indicates a signal line, SCNLindicates a scanning line, AZL indicates an auto zero line, and DRLindicates a drive line. An explanation will be given of the operation ofthis pixel circuit 20 below by referring to the timing charts shown inFIGS. 4A to 4E.

As shown in FIGS. 4A and 4B, the drive line DRL and the auto zero lineAZL are made a high level, and the TFT 22 and TFT 23 are made aconductive state. At this time, the TFT 21 is connected to the lightemitting element (OLED) 25 in a diode connected state, therefore acurrent flows in the TFT 21.

Next, as shown in FIG. 4A, the drive line DRL is made a low level, andthe TFT 22 is made a nonconductive state. At this time, when thescanning line SCNL is the high level, the TFT 24 is made conductive asshown in FIG. 4C, and a reference potential Vref is given to the signalline SGL as shown in FIG. 4D. The current flowing in the TFT 21 is shutoff, therefore, as shown in FIG. 4E, a gate potential Vg of the TFT 21rises, but the TFT 21 becomes the nonconductive state at the point oftime when the potential rises up to VDD−|Vth|, so the potential isstabilized. This operation will be referred to as an “auto zerooperation” below.

As shown in FIGS. 4B and 4D, the auto zero line AZL is made the lowlevel, the TFT 23 is made the nonconductive state, and the potential ofthe signal line SGL is made a voltage lower than Vref by exactly ΔVdata.The change of this signal line potential lowers the gate potential ofthe TFT 21 by exactly ΔVg via the capacitor C21.

As shown in FIGS. 4A and 4C, when the scanning line SCNL is made the lowlevel and the TFT 24 is made nonconductive, the drive line DRL is madethe high level, the TFT 22 is made conductive, current flows in the TFT21 and the light emitting element (OLED) 25, and the light emittingelement 25 starts light emission.

When it is possible to ignore the parasitic capacitance, ΔVg and thegate potential Vg of the TFT 21 become as follows:

ΔVg=ΔVdata×C1/(C1+C2)   (2)

Vg=V _(cc) −|Vth|−ΔVdata×C1/(c1+C2)   (3)

Here, C1 indicates the capacitance value of the capacitor C21, and C2indicates the capacitance value of the capacitor C22.

On the other hand, when the current flowing in the light emittingelement (OLED) 25 at the time of the light emission is Ioled, thecurrent value of this is controlled by the TFT 21 connected in series tothe light emitting element 25. Assuming that the TFT 21 is operating ina saturated region, the following relationship is obtained by a wellknown equation of a MOS transistor and the above Equation (3):

$\begin{matrix}\begin{matrix}{{Ioled} = {\mu \; {{{CoxW}/L}/2}\left( {V_{cc} - {Vg} - {{Vth}}} \right)^{2}}} \\{= {\mu \; {{{CoxW}/L}/2}\left( {\Delta \; {Vdata} \times C\; {1/\left( {{C\; 1} + {C\; 2}} \right)}} \right)^{2}}}\end{matrix} & (4)\end{matrix}$

Here, μ indicates the mobility of the carriers, Cox indicates the gatecapacitance per unit area, W indicates the gate width, and L indicatesthe gate length.

According to Equation (4), Ioled is not controlled according to thethreshold value Vth of the TFT 21, but by ΔVdata given from the outside.In other words, when the pixel circuit 20 of FIG. 3 is used, it ispossible to realize a display device having a relatively high uniformityof the current and consequently uniformity of the luminance withoutinfluence of the threshold value Vth which varies for each pixel.

SUMMARY OF THE INVENTION

Focusing now on the issues to be dealt with in the present invention,since an organic EL element is current light emission type, it isnecessary to supply a large current to the light emitting elements fordisplay, so power supply potential lines become necessary other than thesignal lines and the scanning lines for the individual pixels. Ingeneral, as shown in FIG. 1, when arranging matrix type pixel circuits,as shown in FIG. 5 and FIG. 6, they are arranged in a matrix byrepeating pixel circuits having the same configuration and layout. Notethat, in FIG. 5, the capacitors are omitted for simplification of thefigure.

However, in the circuit arrangements shown in FIG. 5 and FIG. 6, it isnecessary to provide power supply potential lines VCCL1 to VCCLn forsupplying the power supply voltage VCC to the different pixel circuitcolumns. It is not possible to make the lines too wide due to theconstraints in the circuit area. Further, as shown in FIG. 6, top sidesof the plurality of power supply potential lines VCCL are not madecommon, therefore a potential difference arises between the tops andbottoms of the lines. As a result, as shown in FIG. 6, uneven luminancearises between the top and bottom of a screen.

On the other hand, generally a data signal is written into a voltagewrite type pixel circuit as follows. An explanation will be given of 1Hperiod (horizontal scanning period) where the scanning line SCNL (M) isON with reference to FIGS. 7A to 7E.

(1) A signal SCAN(M) for controlling the writing of the data signal fromthe signal line SGL(n) (n=N to N+2) into the pixel circuit “Pixel(M,N)”is made on for the 1H period. Namely, the data signal is written fromthe signal line into the pixel circuit for 1H period.

(2) On the other hand, by turning on the switches 2-N and 2-(N+1) and2-(N+2) for controlling the writing of the data into the signal line foronly part of 1H, the writing of the data into a plurality of signallines is carried out in a time division manner.

In this case, when employing a circuit configuration as shown in FIG. 8for the pixel circuit 10, there inevitably arises a situation where thesignal lines SGL(N+1) and SGL(N+2) end up adjacent between adjacentpixels, therefore, the following problems arise.

Namely, when the signal line SGL(N+1) and signal line SGL(N+2) areadjacent, a selector switch 2-(N+1) turns on so the data is written intothe signal line SGL(N+1), next the select switch 2-(N+1) turns OFF andthe select switch 2-(N+2) turns ON so the data is written into thesignal line SGL(N+2). At this time, since the signal line SGL(N+1) andthe signal line SGL(N+2) are adjacent, a parasitic capacitanceCp(N+1,N+2) is formed. Accordingly, when the data of the signal lineSGL(N+2) is written, the signal line potential of the signal lineSGL(N+1) fluctuates, that is, the data is rewritten. Further, whenrewriting this signal line SGL(N+1), the signal SCAN(M) is ON, thereforethe rewriting of the data is reflected upon the pixel circuit“Pixel(M,N+1)”.

As a result, in an arrangement where the signal lines between pixels areadjacent, rewriting of data between signal lines (crosstalk) occurs,therefore it is difficult to rewrite correct luminance data. Further,the above example was explained by using typical pixel circuits of anorganic EL display device, but the same is also true for an organic ELdisplay device using other pixel circuits for writing luminance datafrom the signal lines. Further, the same is also true for a liquidcrystal display device using LCDs or other pixel circuits for writingluminance data from the signal lines.

Further, as mentioned above, when using pixel circuits 10 as shown inFIG. 2, due to the variation of the threshold value Vth of thetransistors, the uniformity of the luminance between pixels is degraded,so it is difficult to form a high quality display device.

On the other hand, when using pixel circuits of FIG. 3, it is possibleto realize a display device having a relatively high uniformity ofluminance, but this has the following problems:

A first problem is that a gate amplitude ΔVg of the drive transistor isreduced according to Equation (2) from the data amplitude ΔVdata drivenfrom the outside. Seen from another angle, it is necessary to give alarge ΔVdata in order to obtain the same ΔVg. This is undesirable in thepoints of power consumption and noise.

A second problem is that the explanation of operation concerning thepixel circuit 20 of FIG. 3 is only theoretical. In practice, theinfluence of the variation of Vth of the TFTs 21 for driving the lightemitting elements (OLEDs) 25 may not be eliminated. This is because theauto zero line AZL and the gate node of each TFT 21 are coupled by thegate capacitance of the TFT 23. When the auto zero line AZL shifts tothe high level and the TFT 23 becomes nonconductive, the channel chargeof the TFT 23 flows into the gate node of the TFT 21. The reason forthis will be explained next.

Namely, after the end of an auto zero operation, the gate potential ofthe TFT 21 ideally should be VDD−|Vth|, but it becomes a potentialslightly higher than that due to the inflow of the charge. The amount ofinflow of charge fluctuates according to the value of Vth. This isbecause the gate potential of the TFT 21 immediately before the end ofthe auto zero operation is substantially VDD−|Vth|. Accordingly, forexample, the smaller the |Vth|, the higher this potential. On the otherhand, at the time of the end of the auto zero operation, when thepotential of the auto zero line AZL rises and the TFT 23 changes to thenonconductive state, the higher the source potential thereof, that is,the gate potential of the TFT 21, the more delayed the timing when theTFT 23 becomes nonconductive, therefore the larger the amount of chargethat will flow into the gate of the TFT 21. As a result, the gatepotential of the TFT 21 after the end of the auto zero operation isaffected by the |Vth|, so the above Equation (3) and Equation (4)strictly do not stand and are affected by the Vth varying for eachpixel.

Therefore, as a pixel circuit able to compensate for the thresholdvoltage Vth where variation of luminance is particularly liable tobecome a problem, it may be considered to use a threshold voltagecorrection type (offset cancellation type) pixel circuit. In this pixelcircuit, in for example the circuit of FIG. 3, the connection point ofthe drain of the TFT 24 and the coupling capacitor C21 is precharged toa predetermined precharge potential for example for an auto zero period.In this case, the precharge potential line is arranged in the samedirection (in the horizontal direction in FIG. 1) parallel to thescanning line. Generally this offset cancellation operation is carriedout in synchronization with the scanning line. Here, where the number ofpixels of the display is M×N, when using a layout providing theprecharge potential line parallel to the scanning line direction asexplained above, the number of pixels which are simultaneously offsetcancelled by one precharge potential line in the scanning line is N, soN generally becomes several hundreds to thousands or more. Accordingly,as the resolution becomes larger, it becomes more difficult to hold thereference voltage Vpc at a stable potential. Further, when a gradient isformed in this potential between the left and right of the screen, thereis the problem that a gradation is formed in the luminance of thedisplayed image.

It is desirable to provide a display device able to prevent crosstalkbetween pixels by relatively simple layout, able to prevent theoccurrence of uneven luminance in the displayed image, able to stablyand correctly supply a current of a desired value to the light emittingelement of each pixel without regard to the variation of the thresholdvalue of the active elements inside the pixels, and as a result able todisplay a high quality image.

It is further desirable to provide a pixel circuit and a display deviceable to stably and correctly supply a current of a desired value to thelight emitting element of each pixel without regard to the variation ofthe threshold value of the active elements inside the pixels and able tostably hold the reference potential even when an offset cancellationfunction by the precharge potential line is provided and as a resultable to display a high quality image.

According to a first aspect of an embodiment of the present invention,there is provided a display device having at least a plurality of pixelcircuits, connected to signal lines to which data signals in accordancewith luminance information are supplied, arranged in a matrix, whereinpixel circuits of odd number columns and even number columns adjacentsandwiching an axis in a column direction parallel to an arrangementdirection of the signal lines therebetween have a mirror type circuitarrangement symmetric with respect to the axis of the column direction,and a line different from the signal lines is arranged between signallines of adjacent pixel circuits.

Preferably, pixel circuit use signal lines which are adjacent to eachother and do not employ a mirror type circuit arrangement are arrangedso as to be adjacent to each other, and the line different from thesignal lines is arranged between signal lines of adjacent pixel circuitsnot having the mirror type circuit arrangement relationship.

Preferably, the line different from the signal lines is a potential lineheld at a predetermined potential at least while data signals are beingpropagated at adjacent signal lines.

More preferably, power supply potential lines are arranged in the samedirection as the arrangement direction of the signal lines, and twopixel circuits adjacent to each other and employing a mirror typecircuit arrangement relationship share a power supply potential line.

Preferably, the two ends of a plurality of power supply potential linesare connected so as to become common and made the same potential.

Preferably, the device has a function of time-division of the writing ofluminance data information from the signal lines into the pixel circuitsby pixel circuits adjacent sandwiching an axis in the column directionparallel to the arrangement direction of the signal lines.

According to a second aspect of an embodiment of the present invention,there is provided a display device having at least a plurality of pixelcircuits, connected to signal lines to which data signals in accordancewith luminance information are supplied and connected at predeterminednodes to precharge potential lines, arranged in a matrix, wherein pixelcircuits of odd number columns and even number columns adjacentsandwiching an axis in a column direction parallel to an arrangementdirection of the signal lines therebetween have a mirror type circuitarrangement symmetric with respect to the axis of the column direction,and the precharge potential lines are arranged between signal lines ofadjacent pixel circuits.

Preferably, pixel circuit use signal lines which are adjacent to eachother and do not employ a mirror type circuit arrangement are arrangedso as to be adjacent to each other, precharge potential lines are sharedbetween pixel circuits not employing the mirror type circuitarrangement, and shared precharge potential lines are arranged betweensignal lines of adjacent pixel circuits not having the mirror typecircuit arrangement relationship.

According to a third aspect of an embodiment of the present invention,there is provided a display device having a plurality of pixel circuitsarranged in a matrix, signal lines arranged for each column of thematrix array of the pixel circuits and each supplied with at least adata signal in accordance with the luminance information, at least afirst control line and a second control line arranged for each row ofthe matrix array of the pixel circuits, and precharge potential lineseach of which is arranged between signal lines of adjacent pixelcircuits, wherein pixel circuits of odd number columns and even numbercolumns adjacent sandwiching the axis in the column direction parallelto the arrangement direction of the signal lines therebetween have amirror type circuit arrangement symmetric with respect to the axis ofthe column direction, each of the pixel circuits has a first node, asecond node, a drive transistor forming a current supply line between afirst terminal and a second terminal and controlling a current flowingthrough the current supply line in accordance with the potential of thecontrol terminal connected to the second node, a first switch connectedbetween the signal line and the first node and controlled in itsconduction by the first control line, a coupling capacitor connectedbetween the first node and the second node connected to the controlterminal of the drive transistor, and a second switch connected at oneend to a corresponding precharge potential line, connected at the otherend to the first node or the second node, and controlled in itsconduction by the second control line.

According to a fourth aspect of an embodiment of the present invention,there is provided a display device having a plurality of pixel circuitsarranged in a matrix, signal lines arranged for each column of thematrix array of the pixel circuits and each supplied with at least adata signal in accordance with the luminance information, at least afirst control line and a second control line arranged for each row ofthe matrix array of the pixel circuits, and precharge potential lineseach of which is arranged between signal lines of adjacent pixelcircuits, wherein pixel circuits of odd number columns and even numbercolumns adjacent sandwiching the axis in the column direction parallelto the arrangement direction of the signal lines therebetween have amirror type circuit arrangement symmetric with respect to the axis ofthe column direction, each of the pixel circuits has a field effecttransistor, a node, a first switch connected between the source of thefield effect transistor and a first reference potential, a second switchconnected between the source of the field effect transistor and thenode, a third switch connected between the gate of the field effecttransistor and the precharge potential and controlled in its conductionby the second control line, a fourth switch connected between the signalline and the node and controlled in its conduction by the first controlline, and a coupling capacitor connected between the node and the gateof the field effect transistor, the electrooptic element connectedbetween the drain of the field effect transistor and a second referencepotential.

According to a fifth aspect of an embodiment of the present invention,there is provided a display device having a plurality of pixel circuitsarranged in a matrix, signal line arranged for each column with respectto the matrix array of the pixel circuits and each supplied with atleast a data signal in accordance with the luminance information, atleast a first control line and a second control line arranged for eachrow of the matrix array of the pixel circuits, and precharge potentiallines each of which is arranged between signal lines of adjacent pixelcircuits, wherein pixel circuits of odd number columns and even numbercolumns adjacent sandwiching the axis in the column direction parallelto the arrangement direction of the signal lines therebetween have amirror type circuit arrangement symmetric with respect to the axis ofthe column direction, each of the pixel circuits has a field effecttransistor, an electrooptic element, a node, a first switch connectedbetween the source of the field effect transistor and the electroopticelement, a second switch connected between the source of the fieldeffect transistor and the node, a third switch connected between thegate of the field effect transistor and the precharge potential andcontrolled in its conduction by the second control line, a fourth switchconnected between the signal line and the node and controlled in itsconduction by the first control line, and a coupling capacitor connectedbetween the node and the gate of the field effect transistor, the drainof the field effect transistor being connected to a first referencepotential, and the electrooptic element being connected between thefirst switch and a second reference potential.

According to a sixth aspect of an embodiment of the present invention,there is provided a display device having a plurality of pixel circuitsarranged in a matrix, signal lines arranged for each column with respectto the matrix array of the pixel circuits and each supplied with atleast a data signal in accordance with the luminance information, atleast a first control line and a second control line arranged for eachrow of the matrix array of the pixel circuits, and precharge potentiallines each of which is arranged between signal lines of adjacent pixelcircuits, wherein pixel circuits of odd number columns and even numbercolumns adjacent sandwiching the axis in the column direction parallelto the arrangement direction of the signal lines therebetween have amirror type circuit arrangement symmetric with respect to the axis ofthe column direction, each of the pixel circuits has a field effecttransistor, an electrooptic element, a node, a first switch connectedbetween the drain of the field effect transistor and the electroopticelement, a second switch connected between the drain and the gate of thefield effect transistor, a third switch connected between the node andthe precharge potential and controlled in its conduction by the secondcontrol line, a fourth switch connected between the signal line and thenode and controlled in its conduction by the first control line, and acoupling capacitor connected between the node and the gate of the fieldeffect transistor, the source of the field effect transistor beingconnected to the first reference potential, and the electrooptic elementbeing connected between the first switch and the second referencepotential.

Preferably, pixel circuit use signal lines which are adjacent to eachother and do not employ a mirror type circuit arrangement are arrangedso as to be adjacent to each other, precharge potential lines are sharedbetween pixel circuits not employing the mirror type circuitarrangement, shared precharge potential lines are arranged betweensignal lines of adjacent pixel circuits not having the mirror typecircuit arrangement relationship, power supply potential lines arearranged in the same direction as the arrangement direction of thesignal lines, and two pixel circuits adjacent to each other andemploying the mirror type circuit arrangement relationship share thepower supply potential lines.

More preferably, the two ends of a plurality of power supply potentiallines are connected so as to become common and made the same potential.

According to a seventh aspect of an embodiment of the present invention,there is provided a pixel circuit for driving an electrooptic elementchanging in its luminance according to a flowing current, having asignal line to which at least a data signal in accordance with luminanceinformation is supplied, at least a first control line and secondcontrol line, a predetermined precharge potential line, a first node, asecond node, a drive transistor for forming a current supply linebetween a first terminal and a second terminal and controlling thecurrent flowing in the current supply line in accordance with thepotential of the control terminal connected to the second node, a firstswitch connected between the signal line and the first node andcontrolled in its conduction by the first control line, a couplingcapacitor connected between the first node and the second node connectedto the control terminal of the drive transistor, and a second switchconnected at one end to the precharge potential line, connected at theother end to the first node or the second node, and controlled in itsconduction by the second control line, wherein the precharge potentialline is arranged in the same direction parallel to the signal line.

According to an eighth aspect of an embodiment of the present invention,there is provided a pixel circuit for driving an electrooptic elementchanging in its luminance according to a flowing current, having asignal line to which at least a data signal in accordance with luminanceinformation is supplied, first and second reference potentials, apredetermined precharge potential, a field effect transistor, a node, afirst switch connected between the source of the field effect transistorand the first reference potential, a second switch connected between thesource of the field effect transistor and the node, a third switchconnected between the gate of the field effect transistor and theprecharge potential, a fourth switch connected between the signal lineand the node and controlled in its conduction by the first control line,and a coupling capacitor connected between the node and the gate of thefield effect transistor, the electrooptic element being connectedbetween the drain of the field effect transistor and the secondreference potential, and the precharge potential line being arranged inthe same direction so as to be parallel to the signal line.

According to a ninth aspect of an embodiment of the present invention,there is provided a pixel circuit for driving an electrooptic elementchanging in its luminance according to a flowing current, having asignal line to which at least a data signal in accordance with luminanceinformation is supplied, first and second reference potentials, apredetermined precharge potential, a field effect transistor, a node, afirst switch connected between the source of the field effect transistorand the electrooptic element, a second switch connected between thesource of the field effect transistor and the node, a third switchconnected between the gate of the field effect transistor and theprecharge potential, a fourth switch connected between the signal lineand the node and controlled in its conduction by the first control line,and a coupling capacitor connected between the node and the gate of thefield effect transistor, the drain of the field effect transistor beingconnected to the first reference potential, the electrooptic elementbeing connected between the first switch and the second referencepotential, and the precharge potential line being arranged in the samedirection so as to be parallel to the signal line.

According to a 10th aspect of an embodiment of the present invention,there is provided a pixel circuit for driving an electrooptic elementchanging in its luminance according to a flowing current, having atleast a signal line to which a data signal in accordance with luminanceinformation is supplied, at least a first control line, first and secondreference potentials, a predetermined precharge potential, a fieldeffect transistor, a node, a first switch connected between the drain ofthe field effect transistor and the electrooptic element, a secondswitch connected between the drain and gate of the field effecttransistor, a third switch connected between the node and the prechargepotential, a fourth switch connected between the signal line and thenode and controlled in its conduction by the first control line, and acoupling capacitor connected between the node and the gate of the fieldeffect transistor, the source of the field effect transistor beingconnected to the first reference potential, the electrooptic elementbeing connected between the first switch and the second referencepotential, and the precharge potential line being arranged in the samedirection so as to be parallel to the signal line.

According to an 11th aspect of an embodiment of the present invention,there is provided a display device comprised of a plurality of pixelcircuits arranged in a matrix, signal lines arranged for each column ofthe matrix array of the pixel circuits and each supplied with at least adata signal in accordance with luminance information, at least a firstcontrol line arranged for each row of the matrix array of the pixelcircuits, and predetermined precharge potential lines arranged in thesame direction as the signal lines with respect to the matrix array ofthe pixel circuits, wherein each of the pixel circuits has anelectrooptic element, a first node, a second node, a drive transistorfor forming a current supply line between a first terminal and a secondterminal and controlling the current flowing in the current supply linein accordance with the potential of the control terminal connected tothe second node, a first switch connected between the signal line andthe first node and controlled in its conduction by the first controlline, a coupling capacitor connected between the first node and thesecond node connected to the control terminal of the drive transistor,and a second switch connected at one end to a corresponding prechargepotential line, connected at the other end to the first node or thesecond node, and controlled in its conduction by the second controlline.

According to a 12th aspect of an embodiment of the present invention,there is provided a display device comprised of a plurality of pixelcircuits arranged in a matrix, signal lines arranged for each columnwith respect to the matrix array of the pixel circuits and each suppliedwith at least a data signal in accordance with luminance information, atleast a first control line arranged for each row of the matrix array ofthe pixel circuits, predetermined precharge potential lines arranged inthe same direction as the signal lines with respect to the matrix arrayof the pixel circuits, and first and second reference potentials,wherein each of the pixel circuits has a field effect transistor, anelectrooptic element, a node, a first switch connected between thesource of the field effect transistor and the first reference potential,a second switch connected between the source of the field effecttransistor and the node, a third switch connected between the gate ofthe field effect transistor and the precharge potential, a fourth switchconnected between the signal line and the node and controlled in itsconduction by the first control line, and a coupling capacitor connectedbetween the node and the gate of the field effect transistor, theelectrooptic element being connected between the drain of the fieldeffect transistor and a second reference potential.

According to a 13th aspect of an embodiment of the present invention,there is provided a display device comprised of a plurality of pixelcircuits arranged in a matrix, signal lines arranged for each column ofthe matrix array of the pixel circuits and each supplied with a datasignal in accordance with luminance information, at least a firstcontrol line arranged for each row of the matrix array of the pixelcircuits, predetermined precharge potential lines arranged in the samedirection as the signal lines with respect to the matrix array of thepixel circuits, and first and second reference potentials, wherein eachof the pixel circuits has a field effect transistor, an electroopticelement, a node, a first switch connected between the source of thefield effect transistor and the electrooptic element, a second switchconnected between the source of the field effect transistor and thenode, a third switch connected between the gate of the field effecttransistor and the precharge potential, a fourth switch connectedbetween the signal line and the node and controlled in its conduction bythe first control line, and a coupling capacitor connected between thenode and the gate of the field effect transistor, the drain of the fieldeffect transistor being connected to a first reference potential, andthe electrooptic element being connected between the first switch and asecond reference potential.

According to a 14th aspect of an embodiment of the present invention,there is provided a display device comprised of a plurality of pixelcircuits arranged in a matrix, signal lines arranged for each column ofthe matrix array of the pixel circuits and each supplied with at least adata signal in accordance with luminance information, at least a firstcontrol line arranged for each row of the matrix array of the pixelcircuits, predetermined precharge potential lines arranged in the samedirection as the signal lines with respect to the matrix array of thepixel circuits, and first and second reference potentials, wherein eachof the pixel circuits has a field effect transistor, an electroopticelement, a node, a first switch connected between the source of thefield effect transistor and the electrooptic element, a second switchconnected between the source of the field effect transistor and thenode, a third switch connected between the node and the prechargepotential, a fourth switch connected between the signal line and thenode and controlled in its conduction by the first control line, and acoupling capacitor connected between the node and the gate of the fieldeffect transistor, the source of the field effect transistor beingconnected to the first reference potential, and the electrooptic elementbeing connected between the first switch and the second referencepotential.

According to the embodiment of the present invention, for example fixedpotential lines are arranged in the same direction so as to be parallelto the signal lines. Due to this, adjacent signal lines are shielded bythe fixed potential lines, electromagnetic coupling between adjacentsignal lines is blocked, and crosstalk does not occur. As a result, thecorrect luminance data is written.

Further, the precharge potential lines are arranged in the samedirection so as to be parallel to the signal lines. In this case, thenumber of pixels which are connected to one of the precharge potentiallines arranged in the same direction as the signal lines andsimultaneously offset cancelled is for example K. Usually, K is theoffset cancellation period and a time necessary for a sufficient offset.It is usually 1 to several tens or less or small in comparison with thenumber of pixels which are simultaneously cancelled. Further, even whenthe resolution of the panel rises, K does not change. Accordingly, itbecomes easy to hold the precharge potential at a stable potential.Further, it is also possible to share precharge lines of L pixelsadjacent in the parallel direction to the scanning lines. In this case,the number of pixels connected to one of the precharge lines parallel tothe signal lines and simultaneously offset cancelled is K×L. At thistime, for L, a suitable value within a range where it is possible tohold the precharge line at the stable potential may be selected.

Further, the first switch, the second switch, and the third switch aremade the conductive state by for example a predetermined control line.At this time, the control terminal of the drive transistor, for example,the gate, becomes the precharge potential Vpc by the third switch, andan input side potential (node potential) of the coupling capacitor risesto the first reference potential (power supply potential V_(cc)) or nearit since the first and second switches are in the conductive state.Then, the first switch is made the nonconductive state by thepredetermined control line. By this, the current flowing in the drivetransistor is shut off, therefore the potential of the second terminal(for example drain) of the drive transistor falls, but the drivetransistor becomes the nonconductive state at a point of time when thepotential falls to Vpc+|Vth|, and the potential is stabilized. At thistime, the input side potential (node potential) of the capacitor isstill Vpc+|Vth| since the second switch is in the conductive state.Here, |Vth| is an absolute value of the threshold value of the drivetransistor. Next, the second and third switches are made thenonconductive state by the predetermined control line. Alternatively,after making the second switch the nonconductive state, the third switchis made the nonconductive state by the predetermined control line. Thepotential of the input side node of the capacitor is Vpc+|Vth|, and thegate potential of the drive transistor is Vpc. Namely, the potentialdifference between terminals of the capacitor becomes |Vth|. Then, thefourth switch is made the conductive state, and the potential Vdata inaccordance with the luminance data is given from the signal line to theinput side node of the capacitor. The potential difference betweenterminals of the capacitor is held at |Vth| as it is, therefore, thegate potential of the drive transistor becomes Vdata−|Vth|. Next, whenthe fourth switch is made the nonconductive state, and the first switchis made the conductive state by the predetermined control line, thecurrent flows in the drive transistor and the electrooptic element tostart the light emission.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments given with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram of a general active matrix type organic ELdisplay (display device);

FIG. 2 is a circuit diagram of a first example of the configuration of ageneral pixel circuit;

FIG. 3 is a circuit diagram of a second example of the configuration ofa general pixel circuit;

FIGS. 4A to 4E are timing charts for explaining a drive method of thecircuit of FIG. 3;

FIG. 5 is a circuit diagram for explaining an issue in the presentinvention;

FIG. 6 is a view of a layout of power supply potential lines forexplaining this issue in the present invention;

FIGS. 7A to 7E are diagrams for explaining a write operation ofluminance data;

FIG. 8 is a view for explaining an issue in the case of a mirror typecircuit arrangement;

FIG. 9 is a circuit diagram of an active matrix type organic EL display(display device) according to a first embodiment of the presentinvention;

FIG. 10 is a diagram of a layout of power supply lines of the activematrix type organic EL display according to the first embodiment;

FIG. 11 is a circuit diagram of an active matrix type organic EL display(display device) according to a second embodiment of the presentinvention;

FIG. 12 is a diagram of a layout of power supply lines of the activematrix type organic EL display according to the second embodiment;

FIG. 13 is a circuit diagram of an active matrix type organic EL display(display device) according to a third embodiment of the presentinvention;

FIGS. 14A to 14F are timing charts for explaining the operation of thepixel circuit of FIG. 13;

FIG. 15 is a circuit diagram of an active matrix type organic EL display(display device) according to a fourth embodiment of the presentinvention;

FIGS. 16A to 16F are timing charts for explaining the operation of thepixel circuit of FIG. 15;

FIG. 17 is a circuit diagram of an active matrix type organic EL display(display device) according to a fifth embodiment of the presentinvention;

FIG. 18 is a diagram of a layout of power supply lines of the activematrix type organic EL display according to the fifth embodiment;

FIG. 19 is a circuit diagram of an active matrix type organic EL display(display device) according to a sixth embodiment of the presentinvention;

FIG. 20 is a circuit diagram of an active matrix type organic EL display(display device) according to a seventh embodiment of the presentinvention;

FIG. 21 is a circuit diagram of an active matrix type organic EL display(display device) according to an eighth embodiment of the presentinvention; and

FIG. 22 is a diagram of a layout of power supply lines of the activematrix type organic EL display according to the eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, embodiments of the present invention will be described withreference to the accompanying drawings.

First Embodiment

FIG. 9 is a circuit diagram of an active matrix type organic EL display(display device) according to a first embodiment of the presentinvention. Further, FIG. 10 is a diagram of a layout of power supplylines of the active matrix type organic EL display according to thefirst embodiment.

The present organic EL display 100 has, as shown in FIG. 9, a pixelarray 102 including pixel circuits 101 arranged in an m×n matrix, a datadriver (DDRV) 103, and a scan driver (SDRV) 104. n number of columns'worth of signal lines SGL1 to SGLn driven by the data driver (DDRV) 103are arranged for each pixel column of the matrix array of the pixelcircuits 101, while m number of rows' worth of scanning lines SCNL101 toSCNL10 m selectively driven by the data driver (SDRV) 104 are arrangedfor each pixel row.

Further, in the present embodiment, the power supply potential linesVCCL, as shown in FIG. 10, are made common at the top and bottom of thedisplay region constituted by the pixel array 102 in the figure, thatis, the two ends of the plurality of power supply potential linesVCCL101 to VCCL10 n are connected in common to make the potentials thesame in order to prevent uneven luminance due to the potentialdifference in the length direction occurring between the top and bottomof the power supply potential lines VCCL in the figure.

Further, in the present embodiment, pairs of adjacent pixel circuits inthe same rows between the pixel circuits arranged at the odd numbercolumns and the pixel circuits arranged at the even number columns arearranged symmetric with respect to an axis in the column direction, thatis, a so-called mirror type circuit arrangement is used. These adjacentpixel circuits share power supply potential lines VCCL. The power supplypotential lines are formed thicker than usual. Further, the pixelcircuit signal lines in the even number columns and the pixel circuitsignal lines in the odd number columns are arranged adjacently not in amirror type circuit arrangement. Further, fixed potential lines VCCL arearranged between the pixel circuits in the even number columns and thepixel circuits in the odd number columns not in a mirror type circuitarrangement to suppress occurrence of crosstalk between signal lines.Accordingly, one power supply potential line VCCL is arranged for eachodd column (for each two pixels).

Note that, in the present pixel array 102, the pixel circuits 101 arearranged in an m×n matrix, but FIG. 9 shows an example in which they arearranged in a 2 (=m)×3 (=n) matrix for simplification of the figure.Further, in FIG. 9, the 2×3 pixel circuits are also labeled as the“Pixel (M,N)”, “Pixel (M,N+1)”, “Pixel (M,N+2)”, “Pixel (M+1,N)”, “Pixel(M+1,N+1)”, and “Pixel (M+1,N+2)”.

Next, an explanation will be given of the specific configuration of apixel circuit 101.

The pixel circuit 101 has, as shown in FIG. 9, one p-channel TFT 105,one n-channel TFT 106, an organic EL element 107, and a capacitor C101.

In the pixel circuit “Pixel (M,N)” arranged at the first row and thefirst column of FIG. 9, the source of the TFT 105 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the anode sideof the organic EL element 107, and the cathode of the light emittingelement 107 is connected to the cathode line CSL of a predeterminedpotential (for example, the ground potential). A first electrode of thecapacitor C101 is connected to the gate of the TFT 105 (source of theTFT 106), and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 106 is connected to the gate of the TFT 105, the drain is connectedto the signal line SGL101 arranged at the first column, and the gate isconnected to the scanning line SCNL101 arranged at the first row.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 9, the source of the TFT 105 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the anode sideof the organic EL element 107, and the cathode of the light emittingelement 107 is connected to the cathode line CSL of a predeterminedpotential (for example, the ground potential). A first electrode of thecapacitor C101 is connected to the gate of the TFT 105 (source of theTFT 106), and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 106 is connected to the gate of the TFT 105, the drain is connectedto the signal line SGL102 arranged at the second column, and the gate isconnected to the scanning line SCNL101 arranged at the first row.

In the pixel circuit “Pixel (M,N+2)” arranged at the first row and thirdcolumn of FIG. 9, the source of the TFT 105 used as the drive transistoris connected to the power supply potential line VCCL103 arranged at thethird column, the drain is connected to the anode side of the organic ELelement 107, and the cathode of the light emitting element 107 isconnected to the cathode line CSL of a predetermined potential (forexample, the ground potential). A first electrode of the capacitor C101is connected to the gate of the TFT 105 (source of the TFT 106), and asecond electrode is connected to the power supply potential line VCCL103arranged at the third column. The source of the TFT 106 is connected tothe gate of the TFT 105, the drain is connected to the signal lineSGL103 arranged at the third column, and the gate is connected to thescanning line SCNL101 arranged at the first row.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row and thefirst column of FIG. 9, the source of the TFT 105 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the anode sideof the organic EL element 107, and the cathode of the light emittingelement 107 is connected to the cathode line CSL of a predeterminedpotential (for example, the ground potential). A first electrode of thecapacitor C101 is connected to the gate of the TFT 105 (source of theTFT 106), and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 106 is connected to the gate of the TFT 105, the drain is connectedto the signal line SGL101 arranged at the first column, and the gate isconnected to the scanning line SCNL102 arranged at the second row.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andthe second column of FIG. 9, the source of the TFT 105 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the anode sideof the organic EL element 107, and the cathode of the light emittingelement 107 is connected to the cathode line CSL of a predeterminedpotential (for example, the ground potential). A first electrode of thecapacitor C101 is connected to the gate of the TFT 105 (source of theTFT 106), and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 106 is connected to the gate of the TFT 105, the drain is connectedto the signal line SGL102 arranged at the second column, and the gate isconnected to the scanning line SCNL102 arranged at the second row.

In the pixel circuit “Pixel (M+1,N+2)” arranged at the second row andthird column of FIG. 9, the source of the TFT 105 used as the drivetransistor is connected to the power supply potential line VCCL103arranged at the third column, the drain is connected to the anode sideof the organic EL element 107, and the cathode of the light emittingelement 107 is connected to the cathode line CSL of a predeterminedpotential (for example, the ground potential). A first electrode of thecapacitor C101 is connected to the gate of the TFT 105 (source of theTFT 106), and a second electrode is connected to the power supplypotential line VCCL103 arranged at the third column. The source of theTFT 106 is connected to the gate of the TFT 105, the drain is connectedto the signal line SGL103 arranged at the third column, and the gate isconnected to the scanning line SCNL102 arranged at the second row.

Next, an explanation will be given of the operation of the pixel circuit101 by taking as an example the “Pixel (M,N)” of FIG. 9.

In a pixel circuit for writing the luminance data, the pixel rowincluding the pixel circuit is selected by the scan driver 104 via thescanning line SCNL101, whereby the TFT 106 of the pixel circuit of thatrow (the first row in the present example) turns ON. At this time, theluminance data is supplied from the data driver 103 via the signal lineSGL101 in the form of voltage and written into the capacitor C101 forholding the data voltage through the TFT 106. The luminance data writtenin the capacitor C101 is held over a 1 field period. This held datavoltage is applied to the gate of the TFT 105. Due to this, the TFT 105drives the organic EL element 107 by a current according to the helddata. At this time, gradations of the organic EL element 107 areexpressed by modulating the voltage Vdata (<0) between the gate and thesource of the TFT 105 held by the capacitor C101.

Then, for example, a select switch 1032 of the data driver 103 turns ONand the data is transferred to the signal line SGL102, then the selectswitch 1032 turns OFF, a select switch 1033 turns ON, and the data istransferred to the signal line SGL103. When writing the luminance datainto the adjacent pixel circuits in a time division manner in this way,since there is the power supply potential line VCC(102) of a fixedpotential between the signal line SGL102 and the signal line SGL103,electromagnetic coupling is blocked and crosstalk does not occur. Forthis reason, it becomes possible to write the correct luminance data.

According to the first embodiment, there are the advantages thatcrosstalk between pixels can be prevented with a relatively simplelayout without three-dimensional electromagnetic shielding and itbecomes possible to correctly write the luminance data.

Further, in the first embodiment, the power supply potential lines VCCLare made common at the top and bottom of the display region constitutedby the pixel array 102 in the figure, that is, the two ends of theplurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Accordingly, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring in the figure of the power supplypotential line VCCL.

Note that the pixel circuit 101 of FIG. 9 is an example. The presentembodiment is not limited to this. For example, as mentioned above, itis clear that the TFT 106 is only a switch, so it is also possible toconfigure it by a p-channel TFT or other switch element.

Second Embodiment

FIG. 11 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a second embodiment of the presentinvention. Further, FIG. 12 is a diagram of the layout of the powersupply lines of an active matrix type organic EL display deviceaccording to the second embodiment.

The organic EL display 100A has, as shown in FIG. 11, a pixel array 102Aincluding pixel circuits 101A arranged in an m×n matrix, a data driver(DDRV) 103, and a scan driver (SDRV) 104A. Further, the n number ofcolumns' worth of the signal lines SGL1 to SGLn driven by the datadriver (DDRV) 103 are arranged for each pixel column of the matrix arrayof the pixel circuits 101A, and m number of rows' worth of the scanninglines SCNL101 to SCNL10 m, drive lines DRL101 to DRL10 m, and auto zerolines AZL101 to AZL10 m selectively driven by the scan driver (SDRV)104A are arranged for each pixel row.

Further, in the present embodiment, n number of columns' worth of powersupply potential lines VCCL101 to VCCL10 n for supplying the powersupply voltage Vcc and n number of columns' worth of precharge potentiallines VPCL101 to VPCL10 n for supplying the reference voltage Vpc foroffset cancellation are arranged for each pixel column in the samedirection so as to be parallel to the signal lines SGL101 to SGL10 n.

Further, in the present embodiment, the power supply potential linesVCCL, as shown in FIG. 12, are made common at the top and bottom of thedisplay region constituted by the pixel array 102A in the figure, thatis, the two ends of the plurality of power supply potential linesVCCL101 to VCCL10 n are connected in common to make the potentials thesame in order to prevent uneven luminance due to the potentialdifference in the length direction occurring between the top and bottomof the power supply potential lines VCCL in the figure.

Further, in the present embodiment, pairs of adjacent pixel circuits inthe same rows between the pixel circuits arranged at the odd numbercolumns and the pixel circuits arranged at the even number columns arearranged symmetric with respect to an axis in the column direction, thatis, a so-called mirror type circuit arrangement is used. These adjacentpixel circuits share power supply potential lines VCCL. The power supplypotential lines are formed thicker than usual. Further, the pixelcircuit signal lines in the even number columns and the pixel circuitsignal lines in the odd number columns are arranged adjacently not in amirror type circuit arrangement. Further, precharge potential lines VPCLare arranged between the pixel circuits in the even number columns andthe pixel circuits in the odd number columns not in a mirror typecircuit arrangement to suppress occurrence of crosstalk between signallines. Accordingly, one power supply potential line VCCL is arranged foreach odd column (for each two pixels).

Note that, in the present pixel array 102A, the pixel circuits 101A arearranged in an m×n matrix, but FIG. 11 shows an example in which theyare arranged in a 2 (=m)×3 (=n) matrix for simplification of the figure.Further, in FIG. 11, the 2×3 pixel circuits are also indicated as the“Pixel (M,N)”, “Pixel (M,N+1)”, “Pixel (M,N+2)”, “Pixel (M+1,N)”, “Pixel(M+1,N+1)”, and “Pixel (M+1,N+2)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101A.

The pixel circuit 101A has, as shown in FIG. 11, one p-channel TFT 111,four n-channel TFTs 112 to 115, an organic EL element 116, capacitorsC111 and C112, and nodes ND111 to ND113.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL101arranged at the first row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 115 is connected to the node ND112, and thedrain is connected to the precharge potential line VPCL101 arranged atthe first column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL101arranged at the first row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 115 is connected to the node ND112, and thedrain is connected to the precharge potential line VPCL102 arranged atthe second column.

In the pixel circuit “Pixel (M,N+2)” arranged at the first row and thirdcolumn of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL103arranged at the third column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL101arranged at the first row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL103 arranged at the third column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL103 arranged at the third column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 115 is connected to the node ND112, and thedrain is connected to the precharge potential line VPCL102 arranged atthe second column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL102arranged at the second row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 115 is connected to the node ND112,and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andsecond column of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND112 (gateof the TFT 111), and the gate is connected to the auto zero line AZL102arranged at the second row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 115 is connected to the node ND112,and the drain is connected to the precharge potential line VPCL102arranged at the second column.

In the pixel circuit “Pixel (M+1,N+2)” arranged at the second row andthird column of FIG. 11, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL103arranged at the third column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND112 (gateof the TFT 111), and the gate is connected to the auto zero line AZL102arranged at the second row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL103 arranged at the third column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL103 arranged at the third column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 115 is connected to the node ND112,and the drain is connected to the precharge potential line VPCL102arranged at the second column.

Next, an explanation will be given of the operation of the pixel circuit101A by taking as an example the “Pixel (M,N)” of FIG. 11.

The drive line DRL101 and the auto zero line AZL101 are made the highlevel, and the TFT 112, TFT 113, and TFT 115 are made the conductivestate. At this time, the TFT 111 is connected to the light emittingelement (OLED) 116 in the diode-connected state, therefore a constantcurrent Iref flows in the TFT 111. Further, the fixed reference voltageVpc supplied to the precharge potential line VPCL101 is supplied to thenode ND112 of one end (second electrode side) of the coupling capacitorC111 through the TFT 115. Then, a voltage the same as the potentialbetween the gate and the source when the current Iref flows in the TFT111 used as the drive transistor is produced at the two ends of thecoupling capacitor C111. This potential Vref is represented by thefollowing equation defining the gate side of the TFT 111 used as thedrive transistor as the plus direction.

Iref=β(Vref−Vth)²   (5)

Here, β is a proportional coefficient of the drive transistor (∝mobility of the drive transistor), and Vth is the threshold voltage ofthe drive transistor. Namely, the potential Vref between the gate andthe source of the TFT 111 used as the drive transistor becomes asfollows. Note that Iref may be equal to 0 as well.

Vref=Vth+(Iref/β)^(1/2)   (6)

Next, the drive line DRL101 is made the low level, and the TFT 112 ismade nonconductive. At this time, the TFT 114 is made the conductivestate when the scanning line SCNL101 is at the high level, and thereference potential Vref is given to the signal line SGL101. The currentflowing in the TFT 111 is shut off, therefore the gate potential Vg ofthe TFT 111 rises, but at a point of time when the potential rises up toVcc−|Vth|, the TFT 111 becomes the nonconductive state and the potentialis stabilized. Namely, the auto zero operation is carried out.

The auto zero line AZL101 is made the low level to make the TFT 113 thenonconductive state, and the data voltage Vdata is written into theother end side (node ND111 side) of the coupling capacitor C111 throughthe signal line SGL101. Accordingly, the gate-source potential of thedrive transistor at this time is expressed as follows:

Vgs=Vdata+Vref−Vsource

=Vdata+Vth+(Iref/β)^(1/2) −Vsource   (7)

Accordingly, the current Ids flowing in the drive transistor becomes asfollows.

Ids=β(Vdata+(Iref/β)^(1/2) −Vsource)²   (8)

Namely, the current Ids flowing in the drive transistor does not dependupon the threshold voltage Vth. Namely, the threshold voltage iscorrected.

Note that, in order to start the light emission by the light emittingelement 116, after fetching the data voltage, the operation of makingthe scanning line SCNL101 the low level to make the TFT 114 thenonconductive state and making the drive line DRL101 the high level tomake the TFT 112 the conductive state is carried out.

Here, the timing of the offset cancellation will be considered. In thepresent embodiment, the precharge potential lines VPCL are arrangedparallel to the signal lines SGL. At this time, the number of pixelsconnected to one of the precharge potential lines VPCL parallel to thesignal lines SGL and simultaneously offset cancelled is K. Usually, K isthe offset cancellation period and the time necessary for the sufficientoffset. It is usually 1 to several tens or less and small in comparisonwith the number of pixels simultaneously offset cancelled in the relatedart. Further, even when the resolution of the panel rises, K does notchange. Accordingly, it becomes easy to hold the precharge potential atthe stable potential.

Then, for example a select switch 1032 of the data driver becomes ON andthe data is transferred to the signal line SGL102, then a select switch1032 turns OFF, a select switch 1033 turns ON, and the data istransferred to the signal line SGL103. When the luminance data iswritten into adjacent pixel circuits in a time division manner in thisway, since there is a precharge potential line VPCL of the fixedpotential between the signal line SGL102 and the signal line SGL103,electromagnetic coupling is blocked and crosstalk does not occur. Forthis reason, it becomes possible to write the correct luminance data.

According to the second embodiment, in the same way as the effect of thefirst embodiment explained above, there are the advantages that it ispossible that crosstalk between pixels can be prevented with arelatively simple layout without three-dimensional electromagneticshielding and it becomes possible to correctly write the luminance data.

Further, according to the second embodiment, since n number of columns'worth of the power supply potential lines VCCL101 to VCCL10 n forsupplying the power voltage Vcc and n number of columns' worth of theprecharge potential lines VPCL101 to VPCL10 n for supplying thereference voltage Vpc for offset cancellation are arranged for eachpixel column in the same direction so as to be parallel to the signallines SGL101 to SGL10 n, it is possible to stably and correctly supply acurrent of the desired value to the light emitting element of each pixelwithout regard as to variation of the threshold value of the activeelements inside the pixels, it is possible to stably hold the referencepotential even when there is an offset cancellation function by theprecharge potential line, and it is possible to prevent a gradient frombeing formed in the luminance of the displayed image. As a result, it ispossible to display a high quality image.

Further, the power supply potential lines VCCL are made common at thetop and bottom of the display region constituted by the pixel array 102Ain the figure, that is, the two ends of the plurality of power supplypotential lines VCCL101 to VCCL10 n are connected in common to make thepotentials the same. Therefore, it is possible to prevent unevenluminance due to the potential difference in the length directionoccurring between the top and bottom of the power supply potential linesVCCL in the figure.

Note that, the pixel circuit 101A of FIG. 11 is an example. The presentembodiment is not limited to this. For example, as mentioned above, theTFT 112 to TFT 115 are only switches, therefore it is clear that it isalso possible to configure all or part of them by p-channel TFTs orother switch elements.

Third Embodiment

FIG. 13 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a third embodiment of the presentinvention.

The difference of the third embodiment from the second embodimentresides in the configuration of a pixel circuit 101B. Below, anexplanation will be given of the configuration and the operation of apixel circuit 101B according to the third embodiment.

Each of the pixel circuits 101B according to the third embodiment has,as shown in FIG. 13, a p-channel TFT 121, n-channel TFT 122 to TFT 125,capacitors C121 and C122, a light emitting element 126 made of anorganic EL element OLED (electrooptic element) 126, and nodes ND121 toND123. Among these components, TFT 121 forms the field effecttransistor, TFT 122 forms the first switch, TFT 123 forms the secondswitch, TFT 125 forms the third switch, TFT 124 forms the fourth switch,and the capacitor C121 forms the capacitor of the present invention.Further, the scanning line SCNL corresponds to the first control line,and the auto zero line AZL corresponds to the second control line. Notethat, the control line turning ON or OFF the TFT 125 used as the thirdswitch may be the third control line different from the auto zero lineAZL as well. Further, the supply line (power supply potential) of thepower voltage V_(cc) corresponds to the first reference potential, andthe potential of the cathode line CSL (for example ground potential GND)corresponds to the second reference potential.

Note that, in the pixel array 102B, pixel circuits 101B are arranged inan m×n matrix. FIG. 13 shows an example in which they are arranged in a2 (=m)×3 (=n) matrix for the simplification of the figure. Further, inFIG. 13, the 2×3 pixel circuits are also labeled as the “Pixel (M,N)”,“Pixel (M,N+1)”, “Pixel (M,N+2)”, “Pixel (M+1,N)”, “Pixel (M+1,N+1)”,and “Pixel (M+1,N+2)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101B.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL101 arranged at the first row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C121 is connected to the nodeND121, and a second electrode is connected to the node ND122. Further, afirst electrode of the capacitor C122 is connected to the node ND122,and a second electrode is connected to the power supply potential lineVCCL101 arranged at the first column. The source of the TFT 124 isconnected to the node ND122, the drain is connected to the signal lineSGL101 arranged at the first column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT125 is connected to the node ND121 (gate of the TFT 121), and the drainis connected to the precharge potential line VPCL101 arranged at thefirst column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL101 arranged at the first row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C121 is connected to the nodeND121, and a second electrode is connected to the node ND122. Further, afirst electrode of the capacitor C122 is connected to the node ND122,and a second electrode is connected to the power supply potential lineVCCL101 arranged at the first column. The source of the TFT 124 isconnected to the node ND122, the drain is connected to the signal lineSGL102 arranged at the second column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT125 is connected to the node ND121 (gate of the TFT 121), and the drainis connected to the precharge potential line VPCL102 arranged at thesecond column.

In the pixel circuit “Pixel (M,N+2)” arranged at the first row and thirdcolumn of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL103 arranged at the third column, and the gate isconnected to the drive line DRL101 arranged at the first row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C121 is connected to the nodeND121, and a second electrode is connected to the node ND122. Further, afirst electrode of the capacitor C122 is connected to the node ND122,and a second electrode is connected to the power supply potential lineVCCL103 arranged at the third column. The source of the TFT 124 isconnected to the node ND122, the drain is connected to the signal lineSGL103 arranged at the third column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT125 is connected to the node ND121 (gate of the TFT 121), and the drainis connected to the precharge potential line VPCL102 arranged at thesecond column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL102 arranged at the second row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL102 arranged at thesecond row. A first electrode of the capacitor C121 is connected to thenode ND121, and a second electrode is connected to the node ND122.Further, a first electrode of the capacitor C122 is connected to thenode ND122, and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 124 is connected to the node ND122, the drain is connected to thesignal line SGL101 arranged at the first column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 125 is connected to the node ND121 (gate of the TFT121), and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andsecond column of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL102 arranged at the second row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL102 arranged at thesecond row. A first electrode of the capacitor C121 is connected to thenode ND121, and a second electrode is connected to the node ND122.Further, a first electrode of the capacitor C122 is connected to thenode ND122, and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 124 is connected to the node ND122, the drain is connected to thesignal line SGL102 arranged at the second column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 125 is connected to the node ND121 (gate of the TFT121), and the drain is connected to the precharge potential line VPCL102arranged at the second column.

In the pixel circuit “Pixel (M+1,N+2)” arranged at the second row andthird column of FIG. 13, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (the connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL103 arranged at the third column, and the gate isconnected to the drive line DRL102 arranged at the second row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL102 arranged at thesecond row. A first electrode of the capacitor C121 is connected to thenode ND121, and a second electrode is connected to the node ND122.Further, a first electrode of the capacitor C122 is connected to thenode ND122, and a second electrode is connected to the power supplypotential line VCCL103 arranged at the third column. The source of theTFT 124 is connected to the node ND122, the drain is connected to thesignal line SGL103 arranged at the third column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 125 is connected to the node ND121 (gate of the TFT121), and the drain is connected to the precharge potential line VPCL102arranged at the second column.

Next, an explanation will be given of the operation of the pixel circuit101B by referring to the timing charts shown in FIGS. 14A to 14E bytaking as an example the “Pixel (M,N)” of FIG. 11.

Step ST11

First, as shown in FIGS. 14A and 14B, the drive line DRL101 and the autozero line AZL101 are made the high level to make the TFT 122, TFT 123,and TFT 125 the conductive state. At this time, the gate of the TFT 121becomes the precharge potential Vpc as shown in FIG. 14F by the TFT 125,and the input side potential VC121 of the capacitor C121 rises up to thepower supply potential V_(cc) or near it as shown in FIG. 14E since theTFT 122 and TFT 123 are in the conductive state.

Step ST12

As shown in FIG. 14A, the drive line DRL101 is made the low level tomake the TFT 122 the nonconductive state. The current flowing in the TFT121 is shut off, therefore the potential of the drain of the TFT 121falls, but at the point of time when the potential falls to VPC+|Vth|,the TFT 121 becomes the nonconductive state and the potential isstabilized. At this time, the input side potential VC121 of thecapacitor C121 is still VPC+|Vth| as shown in FIG. 14E since the TFT 123is in the conductive state. Here, |Vth| is the absolute value of thethreshold value of the TFT 121.

Step ST13

As shown in FIG. 14B, the auto zero line AZL101 is made the low level tomake the TFT 123 and the TFT 125 the nonconductive state. The potentialVC121 of the input side node of the capacitor C121 is VPC+|Vth| as shownin FIG. 14E, and the gate potential Vg121 of the TFT 121 is Vpc as shownin FIG. 14F. Namely, the potential difference between terminals of thecapacitor C121 becomes |Vth|.

Step ST14

As shown in FIGS. 14C and 14D, the scanning line SCNL101 is made thehigh level to make the TFT 124 the conductive state, and the potentialVdata in accordance with the luminance data is given from the signalline SGL101 to the input side node ND121 of the capacitor C121. Thepotential difference between terminals of the capacitor C121 is held at|Vth| as it is, therefore the gate potential Vg121 of the TFT 121becomes Vdata−|Vth| as shown in FIG. 14F.

Step ST15

As shown in FIGS. 14A and 14C, when the scanning line SCNL101 is madethe low level to make the TFT 124 the nonconductive state, the driveline DRL101 is made the high level to make the TFT 122 the conductivestate, the current flows in the TFT 121 and the light emitting element(OLED) 126, and the OLED starts the light emission.

Note that, in the operation of steps ST11 and ST12 described above, itis necessary to set the value of Vpc so that Vpc+|Vth| becomes smallerthan VDD, but the value of Vpc may be any value so far as this issatisfied.

When calculating the current Ioled flowing in the light emitting element(OLED) 126 after the above operation, it becomes as follows if the TFT121 is operating in the saturated region:

Ioled=μCoxW/L/2(Vgs−Vth)²

=μCoxW/L/2(V _(cc) −Vg−|Vth|)²

=μCoxW/L/2(V _(cc) −Vdata+|Vth|−|Vth|)²

=μCoxW/L/2(V _(cc) −Vdata)²   (9)

Here, μ indicates the mobility of the carriers, Cox indicates the gatecapacitance per unit area, W indicates the gate width, and L indicatesthe gate length. According to Equation (9), the current Ioled does notdepend upon the threshold value Vth of the TFT 121 (not according toVth), but is controlled by Vdata given from the outside. In other words,when the pixel circuit 101B of FIG. 13 is used, it is possible torealize a display device not affected by Vth varying for each pixel andhaving relatively high uniformity of current and consequently uniformityof luminance.

Further, even in the case where the TFT 121 is operating in the linearregion, the current Ioled flowing in the light emitting element (OLED)126 becomes as follows and still does not depend upon Vth:

$\begin{matrix}\begin{matrix}{{Ioled} = {\mu \; {Cox}\; {W/L}\left\{ {{\left( {{Vgs} - {Vth}} \right){Vds}} - {{Vds}^{2}/2}} \right\}}} \\{= {\mu \; {Cox}\; {W/L}\left\{ {{\left( {V_{cc} - {Vg} - {{Vth}}} \right)\left( {V_{cc} - {Vd}} \right)} -} \right.}} \\\left. {\left( {V_{cc} - {Vd}} \right)^{2}/2} \right\} \\{= {\mu \; {Cox}\; {W/L}\left\{ {{\left( {V_{cc} - {Vdata} + {{Vth}} - {{Vth}}} \right)\left( {V_{cc} - {Vd}} \right)} -} \right.}} \\\left. {\left( {V_{cc} - {Vd}} \right)^{2}/2} \right\} \\{= {\mu \; {{CoxW}/L}\left\{ {{\left( {V_{cc} - {Vdata}} \right)\left( {V_{cc} - {Vd}} \right)} - {\left( {V_{cc} - {Vd}} \right)^{2}/2}} \right\}}}\end{matrix} & (10)\end{matrix}$

Here, Vd indicates the drain potential of the TFT 121.

As described above, the pixel circuit 101B of the third embodiment ismore excellent than the example of the related art of FIG. 1 in thepoint that the influence of the variation of the threshold value Vth isable to be cancelled. It is more excellent than the example of therelated art of FIG. 3 in the following points. First, in the related artof FIG. 3, there was the problem that the gate amplitude ΔVg of thedrive transistor decreased according to Equation (2) from the dataamplitude ΔVdata driven from the outside, but in the present embodiment,the data amplitude is substantially equal to the gate amplitude,accordingly it is possible to drive the pixel circuit with a smallersignal line amplitude. Due to this, drive by a lower power consumptionand lower noise becomes possible. Second, looking at the capacitancecoupling of the auto zero line and the gate of TFT which becomes aproblem in the related art of FIG. 3, in the pixel circuit 101B of FIG.13, the TFT 123 is not directly connected to the gate of the TFT 121, sothe influence thereof is small. On the other hand, the TFT 125 isconnected to the gate of the TFT 121, but the source of the TFT 125 isconnected to the constant potential Vpc, therefore, even when the gatepotential thereof changes at the time of the end of the auto zerooperation, the gate potential of the TFT 121 is held at the potential ofsubstantially Vpc. In this way, in the pixel circuit 101B of FIG. 13,the influence of coupling between the auto zero line AZL and the gate ofthe TFT 121 is small. As a result, the correction of the variation ofVth is carried out more correctly than the pixel circuit of FIG. 3.Namely, according to the present embodiment, it is possible to realizean organic EL use pixel circuit able to correctly supply current of adesired value to a light emitting element of the pixel circuit withoutregard to the variation of the threshold value of the transistors and asa result able to display a high quality image having a high luminanceuniformity. As a result, correction of the threshold value with a higherprecision than similar circuits in the past becomes possible.

Next, the timing of the offset cancellation will be considered. In thethird embodiment as well, the precharge potential lines VPCL arearranged parallel to the signal lines SGL. At this time, the number ofpixels connected to one of the precharge potential lines VPCL parallelto the signal lines SGL and simultaneously offset cancelled is K.Usually, K is the offset cancellation period and the time necessary forthe sufficient offset. It is usually 1 to several tens or less and smallin comparison with the number of pixels simultaneously offset cancelledin the related art. Further, even when the resolution of the panelrises, K does not change. Accordingly, it becomes easy to hold theprecharge potential at a stable potential.

Then, for example the select switch 1032 of the data driver becomes ONand the data is transferred to the signal line SGL102, then the selectswitch 1032 turns OFF, the select switch 1033 turns ON, and the data istransferred to the signal line SGL103. When the luminance data iswritten into adjacent pixel circuits in a time division manner in thisway, since there is a precharge potential line VPCL of a fixed potentialbetween the signal line SGL102 and the signal line SGL103,electromagnetic coupling is blocked and crosstalk does not occur. Forthis reason, it becomes possible to write the correct luminance data.

According to the third embodiment, in the same way as the effects of thefirst embodiment mentioned above, there are the advantages that it ispossible that crosstalk between pixels can be prevented with arelatively simple layout without three-dimensional electromagneticshielding and it becomes possible to correctly write the luminance data.

Further, according to the third embodiment, there are effects the sameas those by the second embodiment mentioned above, that is, it ispossible to stably and correctly supply current of the desired value tothe light emitting element of each pixel without regard to the variationof the threshold value of the active elements inside the pixels, it ispossible to stably hold the reference potential even when there is anoffset cancellation function by the precharge potential line, and it ispossible to prevent a gradient from being formed in the luminance of thedisplayed image. As a result, there is the advantage that a high qualityimage is able to be displayed.

Further, in the third embodiment as well, the power supply potentiallines VCCL are made common at the top and bottom of the display regionconstituted by the pixel array 102B in the figure, that is, the two endsof the plurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Accordingly, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring between the top and bottom of the powersupply potential lines VCCL in the figure.

Note that the pixel circuit 101B of FIG. 13 is an example, and thepresent embodiment is not limited to this. For example, as mentionedabove, the TFT 122 to TFT 125 are only switches, therefore it is clearthat it is also possible to configure all or part of them by p-channelTFTs or other switch elements.

Fourth Embodiment

FIG. 15 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a fourth embodiment of the presentinvention.

The difference of the fourth embodiment from the above third embodimentresides in the configuration of a pixel circuit 101C. Below, anexplanation will be given of the configuration and the operation of thepixel circuit 101C according to the fourth embodiment.

Each of the pixel circuits 101C according to the fourth embodiment has,as shown in FIG. 15, n-channel TFT 131 to TFT 135, capacitors C131 andC132, a light emitting element 136 made of an organic EL element OLED(electrooptic element) 136, and nodes ND131 to ND133. Among thesecomponents, the TFT 131 forms the field effect transistor, TFT 132 formsthe first switch, TFT 133 forms the second switch, TFT 125 forms thethird switch, and TFT 134 forms the fourth switch. Further, the scanningline SCNL corresponds to the first control line, and the auto zero lineAZL corresponds to the second control line. Note that the control lineturning ON or OFF the TFT 135 used as the third switch may be a thirdcontrol line different from the auto zero line AZL as well. Further, thesupply line (power supply potential) of the power voltage V_(cc)corresponds to the first reference potential, and the potential of thecathode line CSL (for example ground potential GND) corresponds to thesecond reference potential.

Note that, in the present pixel array 102C, the pixel circuits 101C arearranged in an m×n matrix, but FIG. 15 shows an example in which theyare arranged in a 2 (=m)×3 (=n) matrix for simplification of the figure.Further, in FIG. 15, the 2×3 pixel circuits are also labeled as “Pixel(M,N)”, “Pixel (M,N+1)”, “Pixel (M,N+2)”, “Pixel (M+1,N)”, “Pixel(M+1,N+1)”, and “Pixel (M+1,N+2)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101C.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 15, the drain of the TFT 131 used as the drive transistoris connected to the power supply potential line VCCL101 arranged at thefirst column, the source is connected to the node ND133, and the gate isconnected to the node ND131. The drain of the TFT 132 is connected tothe node ND133 (source of the TFT 131), the source is connected to theanode side of the organic EL element 136, the gate is connected to thedrive line DRL101 arranged at the first row, and the cathode of thelight emitting element 136 is connected to the cathode line CSL of apredetermined potential (for example, the ground potential). The sourceof the TFT 133 is connected to the node ND133 (source of the TFT 131),the drain is connected to the node ND132 (source of the TFT 134), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C131 is connected to the nodeND131, and a second electrode is connected to the node ND132. Further, afirst electrode of the capacitor C132 is connected to the node ND132,and a second electrode is connected to the power supply potential lineVCCL101 arranged at the first column. The source of the TFT 134 isconnected to the node ND134, the drain is connected to the signal lineSGL101 arranged at the first column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT135 is connected to the node ND131, and the drain is connected to theprecharge potential line VPCL101 arranged at the first column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 15, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the source is connected to the node ND133,and the gate is connected to the node ND131. The drain of the TFT 132 isconnected to the node ND133 (source of the TFT 131), the source isconnected to the anode side of the organic EL element 136, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 136 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL101 arranged at the first row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 135 is connected to the node ND131, and thedrain is connected to the precharge potential line VPCL102 arranged atthe second column.

In the pixel circuit “Pixel (M,N+2)” arranged at the first row and thirdcolumn of FIG. 15, the drain of the TFT 131 used as the drive transistoris connected to the power supply potential line VCCL103 arranged at thethird column, the source is connected to the node ND133, and the gate isconnected to the node ND131. The drain of the TFT 132 is connected tothe node ND133 (source of the TFT 131), the source is connected to theanode side of the organic EL element 136, the gate is connected to thedrive line DRL101 arranged at the first row, and the cathode of thelight emitting element 136 is connected to the cathode line CSL of apredetermined potential (for example, the ground potential). The sourceof the TFT 133 is connected to the node ND133 (source of the TFT 131),the drain is connected to the node ND132 (source of the TFT 134), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C131 is connected to the nodeND131, and a second electrode is connected to the node ND132. Further, afirst electrode of the capacitor C132 is connected to the node ND132,and a second electrode is connected to the power supply potential lineVCCL103 arranged at the third column. The source of the TFT 134 isconnected to the node ND132, the drain is connected to the signal lineSGL103 arranged at the third column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT135 is connected to the node ND131, and the drain is connected to theprecharge potential line VPCL102 arranged at the second column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 15, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the source is connected to the node ND133,and the gate is connected to the node ND131. The drain of the TFT 132 isconnected to the node ND133 (source of the TFT 131), the source isconnected to the anode side of the organic EL element 136, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 136 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL102 arranged at the second row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 135 is connected to the node ND131,and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andsecond column of FIG. 15, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the source is connected to the node ND133,and the gate is connected to the node ND131. The drain of the TFT 132 isconnected to the node ND133 (source of the TFT 131), the source isconnected to the anode side of the organic EL element 136, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 136 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL102 arranged at the second row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 135 is connected to the node ND131,and the drain is connected to the precharge potential line VPCL102arranged at the second column.

In the pixel circuit Pixel “(M+1,N+2)” arranged at the second row andthird column of FIG. 15, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL103arranged at the third column, the source is connected to the node ND133,and the gate is connected to the node ND131. The drain of the TFT 132 isconnected to the node ND133 (source of the TFT 131), the source isconnected to the anode side of the organic EL element 136, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 113 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL102 arranged at the second row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL103 arranged at the third column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL103 arranged at the third column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 135 is connected to the node ND132,and the drain is connected to the precharge potential line VPCL102arranged at the second column.

The biggest difference between the pixel circuit 101C of FIG. 15 and thepixel circuit 101B of FIG. 13 resides in the point that the TFT 131 usedas the drive transistor for controlling the current flowing in the lightemitting element (OLED) 46 is an n-channel, and the source thereof andthe organic EL element (OLED) are connected via the TFT 132 used as theswitch.

Next, an explanation will be given of the operation of the pixel circuit101C by referring to the timing charts of FIGS. 16A to 16F by taking asan example the “Pixel (M,N)” of FIG. 15.

Step ST21

As shown in FIGS. 16A and 16B, the drive line DRL101 and the auto zeroline AZL101 are made the high level to make the TFT 132, TFT 133, andTFT 135 the conductive state. At this time, the gate potential Vg131 ofthe TFT 131 becomes the precharge potential Vpc as shown in FIG. 16F bythe TFT 135. When the Vpc is made a sufficient high potential, the TFT131 becomes the conductive state, and the current flows in the TFT 131and the light emitting element (OLED) 136.

Step ST22

As shown in FIG. 16A, the drive line DRL is made the low level to makethe TFT 132 the nonconductive state. The current flowing in the TFT 131is shut off, therefore the source potential of the TFT 131 rises, but atthe point of time when the potential rises up to (Vpc−Vth), the TFT 131becomes the nonconductive state and the potential is stabilized. At thistime, the input side potential VC131 of the capacitor C131 is still(Vpc−Vth) as shown in FIG. 16E since the TFT 133 is in the conductivestate. Here, Vth is the absolute value of the threshold value of the TFT131.

Step ST23

As shown in FIGS. 16B, the auto zero line AZL101 is made the low levelto make the TFT 133 and the TFT 135 the nonconductive state. Thepotential VC131 of the input side node ND131 of the capacitor C131 is(Vpc−Vth) as shown in FIG. 16E, and the gate potential Vg131 of the TFT131 is Vpc as shown in FIG. 16F. Namely, the potential differencebetween terminals of the capacitor C131 becomes Vth.

Step ST24

As shown in FIGS. 16C and 16D, the scanning line SCNL101 is made thehigh level to make the TFT 134 the conductive state, and the potentialVdata in accordance with the luminance data is given from the signalline SGL101 to the input side node ND131 of the capacitor C131. Thepotential difference between terminals of the capacitor C131 is held atVth as it is, therefore the gate potential Vg131 of the TFT 131 becomes(Vdata+Vth) as shown in FIG. 16F.

Step ST25

As shown in FIGS. 16A and 16C, when the scanning line SCNL101 is madethe low level to make the TFT 134 the nonconductive state and the driveline DRL101 is made the high level to make the TFT 132 the conductivestate, the current flows in the TFT 131 and the light emitting element(OLED) 136, and the light emitting element (OLED) 136 starts the lightemission.

Note that, in the operation of steps ST21 and ST22 described above, itis necessary to set the value of Vpc so that Vpc−Vth becomes larger thanVth_el when Vth_el is the threshold value of the light emitting element(OLED), but the value of Vpc may be any value so far as this issatisfied.

When calculating the current Ioled flowing in the light emitting element(OLED) 136 after the above operation, it becomes as follows if the TFT131 is operating in the saturated region:

$\begin{matrix}\begin{matrix}{{Ioled} = {\mu \; {{{CoxW}/L}/2}\left( {{Vgs} - {Vth}} \right)^{2}}} \\{= {\mu \; {{{CoxW}/L}/2}\left( {V_{cc} - {Vs} - {Vth}} \right)^{2}}} \\{= {\mu \; {{{CoxW}/L}/2}\left( {{Vdata} + {Vth} - {Vs} - {Vth}} \right)^{2}}} \\{= {\mu \; {{{CoxW}/L}/2}\left( {{Vdata} - {Vs}} \right)^{2}}}\end{matrix} & (11)\end{matrix}$

Here, μ indicates the mobility of the carriers, Cox indicates the gatecapacitance per unit area, W indicates the gate width, and L indicatesthe gate length. According to Equation (11), the current Ioled flowingin the light emitting element (OLED) 136 does not depend upon thethreshold value Vth of the TFT 131, but is controlled by Vdata givenfrom the outside. In other words, when the pixel circuit 101C of FIG. 15is used, it is possible to realize a display device not affected by theVth varying for each pixel and having a relatively high uniformity ofcurrent, consequently uniformity of the luminance. This is true also forthe case where the TFT 131 is operating in the linear region.

Further, for example, when the select switch 1032 of the data driverbecomes ON and the data is transferred to the signal line SGL102, thenthe select switch 1032 turns OFF, the select switch 1033 turns ON, andthe data is transferred to the signal line SGL103, there is a prechargepotential line VPCL102 of the fixed potential between the signal lineSGL102 and the signal line SGL103, therefore electromagnetic coupling isblocked and no crosstalk occurs. For this reason, it becomes possible towrite the correct luminance data.

According to the fourth embodiment, in the same way as the effects ofthe second and third embodiments mentioned above, there are theadvantages that it is possible to prevent crosstalk between pixels by arelatively simple layout without three-dimensional electromagneticshielding and it becomes possible to correctly write the luminance data.

Further, according to the fourth embodiment, there are effects the sameas those by the second and third embodiments mentioned above, that is,it is possible to stably and correctly supply a current of the desiredvalue to the light emitting element of each pixel without regard tovariation of the threshold value of the active elements inside thepixels, it is possible to stably hold the reference potential even whenthere is an offset cancellation function by the precharge potentialline, and it is possible to prevent a gradient from being formed in theluminance of the displayed image. As a result, there is the advantagethat a high quality image is able to be displayed.

Further, in the fourth embodiment as well, the power supply potentiallines VCCL are made common at the top and bottom of the display regionconstituted by the pixel array 102C in the figure, that is, the two endsof the plurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Accordingly, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring between the top and bottom of the powersupply potential lines VCCL in the figure.

Note that, the pixel circuit 101C of FIG. 15 is an example, and thepresent embodiment is not limited to this. For example, as mentionedabove, the TFT 132 to TFT 135 are only switches, therefore it is clearthat it is also possible to configure all or part of them by p-channelTFTs or other switch elements.

In the above, the explanation was given by taking as an example a mirrortype circuit arrangement. In the following description, an explanationwill be given of an example of the configuration of an active matrixtype organic EL display device (display device) not having a mirror typecircuit arrangement.

Fifth Embodiment

FIG. 17 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a fifth embodiment of the presentinvention. Further, FIG. 18 is a diagram of a layout of the power supplylines of the active matrix type organic EL display device according tothe fifth embodiment.

The difference of the organic EL display 100D according to the fifthembodiment from the organic EL display 100A according to the secondembodiment resides in that non-mirror type circuit arrangement isprovided. The rest of the configuration of the organic EL display 100Dis the same as that of the second embodiment, so the same components inFIG. 17 as in FIG. 11 are represented by the same notations.

The organic EL display 100D has, as shown in FIG. 17, a pixel array 102Dincluding pixel circuits 101D arranged in an m×n matrix, a data driver(DDRV) 103, and a scan driver (SDRV) 104. Further, n number of columns'worth of the signal lines SGL101 to SGL10 n driven by the data driver(DDRV) 103 are arranged for each pixel column of the matrix array of thepixel circuits 101D, and m number of rows' worth of the scanning linesSCNL101 to SCNL10 m, drive lines DRL101 to DRV10 m, and auto zero linesAZL101 to AZL10 m selectively driven by the scan driver (SDRV) 104 arearranged for each pixel row.

Further, in the present embodiment, n number of columns' worth of thepower supply potential lines VCCL101 to VCCL10 n for supplying the powervoltage Vcc and n number of columns' worth of precharge potential linesVPCL101 to VPCL10 n for supplying the reference voltage Vpc for theoffset cancellation are arranged for each pixel column in the samedirection so as to be parallel to the signal lines SGL101 to SGL10 n.

Further, in the present embodiment, the power supply potential linesVCCL, as shown in FIG. 18, are made common at the top and bottom of thedisplay region constituted by the pixel array 102D in the figure, thatis, the two ends of the plurality of power supply potential linesVCCL101 to VCCL10 n are connected in common to make the potentials thesame in order to prevent uneven luminance due to the potentialdifference in the length direction occurring between the top and bottomof the power supply potential lines VCCL in the figure.

Note that, in the present pixel array 102D, the pixel circuits 101D arearranged in an m×n matrix, but FIG. 17 shows an example where they arearranged in a 2 (=m)×2 (=n) matrix for simplification of the figure.Further, in FIG. 17, the 2×2 pixel circuits are also labeled as the“Pixel (M,N)”, “Pixel (M,N+1)”, “Pixel (M+1,N)”, and “Pixel (M+1,N+1)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101D.

The pixel circuit 101D basically has the same configuration as that ofthe circuit of FIG. 11. Specifically, the pixel circuit 101D has, asshown in FIG. 17, one p-channel TFT 111, four n-channel TFT 112 to TFT115, an organic EL element 116, capacitors C111 and C112, and nodesND111 to ND113.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 17, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL101arranged at the first row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 115 is connected to the node ND112, and thedrain is connected to the precharge potential line VPCL101 arranged atthe first column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 17, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL102arranged at the second row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 115 is connected to the node ND112,and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 17, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL102arranged at the second column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 113 is connected to the node ND113(drain of the TFT 111), the drain is connected to the node ND111 (gateof the TFT 111), and the gate is connected to the auto zero line AZL101arranged at the first row. A first electrode of the capacitor C111 isconnected to the node ND111, and a second electrode is connected to thenode ND112. Further, a first electrode of the capacitor C112 isconnected to the node ND111, and a second electrode is connected to thepower supply potential line VCCL102 arranged at the second column. Thesource of the TFT 114 is connected to the node ND112, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 115 is connected to the node ND112, and thedrain is connected to the precharge potential line VPCL102 arranged atthe second column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andsecond column of FIG. 17, the source of the TFT 111 used as the drivetransistor is connected to the power supply potential line VCCL102arranged at the second column, the drain is connected to the node ND113,and the gate is connected to the node ND111. The drain of the TFT 112 isconnected to the node ND113 (drain of the TFT 111), the source isconnected to the anode side of the organic EL element 116, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 116 is connected to the cathodeline CSL of a predetermined potential (for example, ground potential).The source of the TFT 113 is connected to the node ND113 (drain of theTFT 111), the drain is connected to the node ND111 (gate of the TFT111), and the gate is connected to the auto zero line AZL102 arranged atthe second row. A first electrode of the capacitor C111 is connected tothe node ND111, and a second electrode is connected to the node ND112.Further, a first electrode of the capacitor C112 is connected to thenode ND111, and a second electrode is connected to the power supplypotential line VCCL102 arranged at the second column. The source of theTFT 114 is connected to the node ND112, the drain is connected to thesignal line SGL102 arranged at the second column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 115 is connected to the node ND112, and the drain isconnected to the precharge potential line VPCL102 arranged at the secondcolumn.

The operation of the pixel circuit 101D is basically the same as that ofthe circuit of FIG. 11, so a detailed explanation is omitted here.

Here, the timing of the offset cancellation will be considered. In thefifth embodiment, the precharge potential lines VPCL are arrangedparallel to the signal lines SGL. At this time, the number of pixelsconnected to one of the precharge potential lines VPCL parallel to thesignal lines SGL and simultaneously offset cancelled is K. Usually, K isthe offset cancellation period and the time necessary for the sufficientoffset. It is usually 1 to several tens or less and small in comparisonwith the number of pixels simultaneously offset cancelled in the relatedart. Further, even when the resolution of the panel rises, K does notchange. Accordingly, it becomes easy to hold the precharge potential ata stable potential.

As explained above, according to the fifth embodiment, n number ofcolumns' worth of the power supply potential lines VCCL101 to VCCL10 nfor supplying the power voltage Vcc and n number of columns' worth ofthe precharge potential lines VPCL101 to VPCL10 n for supplying thereference voltage Vpc for the offset cancellation are arranged for eachpixel column in the same direction so as to be parallel to the signallines SGL101 to SGL10 n, therefore it is possible to stably andcorrectly supply a current of the desired value to the light emittingelement of each pixel without regard to the variation of the thresholdvalue of the active elements inside the pixels, it is possible to stablyhold the reference potential even when there is an offset cancellationfunction by the precharge potential line, and it is possible to preventa gradient from being formed in the luminance of the displayed image. Asa result, it is possible to display a high quality image.

Further, in the fifth embodiment, the power supply potential lines VCCLare made common at the top and bottom of the display region constitutedby the pixel array 102D in the figure, that is, the two ends of theplurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Therefore, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring between the top and bottom of the powersupply potential lines VCCL in the figure.

Note that the pixel circuit 101D of FIG. 17 is an example, and thepresent embodiment is not limited to this. For example, as mentionedabove, the TFT 112 to TFT 115 are only switches, therefore it is clearthat it is also possible to configure all or part of them by p-channelTFTs or other switch elements.

Sixth Embodiment

FIG. 19 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a sixth embodiment of the presentinvention.

The difference of the organic EL display 100E according to the sixthembodiment from the organic EL display 100B according to the secondembodiment resides in that a non-mirror type circuit arrangement isprovided. The rest of the configuration of the organic EL display 100Eis the same as that of the third embodiment, so the same components ofFIG. 19 as in FIG. 13 are represented by the same notations.

Each pixel circuit 101E according to the sixth embodiment has, as shownin FIG. 19, a p-channel TFT 121, n-channel TFT 122 to TFT 125,capacitors C121 and C122, a light emitting element 126 made of anorganic EL element (electrooptic element), and nodes ND121 to ND123.Among these components, the TFT 121 forms the field effect transistor,TFT 122 forms the first switch, TFT 123 forms the second switch, TFT 125forms the third switch, and TFT 124 forms the fourth switch. Further,the scanning line SCNL corresponds to the first control line. Note thatthe auto zero line AZL is commonly used as the control line for turningON or OFF the TFT 125, but it is also able to perform the ON/OFF controlby using another control line. Further, the supply line (power supplypotential) of the power voltage V_(cc) corresponds to the firstreference potential, and the potential of the cathode line CSL (forexample the ground potential GND) corresponds to the second referencepotential.

Note that, in the pixel array 102E, the pixel circuits 101E are arrangedin an m×n matrix, but in FIG. 19, an example of arranging them in a 2(=m)×2 (=n) matrix is shown for simplification of the drawing. Further,in FIG. 19, the 2×2 pixel circuits are also labeled as “Pixel (M,N)”,“Pixel (M,N+1)”, “Pixel (M+1,N)”, and “Pixel (M+1,N+1)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101E.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 19, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL101 arranged at the first row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C121 is connected to the nodeND121, and a second electrode is connected to the node ND122. Further, afirst electrode of the capacitor C122 is connected to the node ND122,and a second electrode is connected to the power supply potential lineVCCL101 arranged at the first column. The source of the TFT 124 isconnected to the node ND122, the drain is connected to the signal lineSGL101 arranged at the first column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT125 is connected to the node ND121 (gate of the TFT 121), and the drainis connected to the precharge potential line VPCL101 arranged at thefirst column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 19, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL101 arranged at the first column, and the gate isconnected to the drive line DRL102 arranged at the second row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL102 arranged at thesecond row. A first electrode of the capacitor C121 is connected to thenode ND121, and a second electrode is connected to the node ND122.Further, a first electrode of the capacitor C122 is connected to thenode ND122, and a second electrode is connected to the power supplypotential line VCCL101 arranged at the first column. The source of theTFT 124 is connected to the node ND122, the drain is connected to thesignal line SGL101 arranged at the first column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 125 is connected to the node ND121 (gate of the TFT121), and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 19, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL102 arranged at the second column, and the gate isconnected to the drive line DRL101 arranged at the first row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C121 is connected to the nodeND121, and a second electrode is connected to the node ND122. Further, afirst electrode of the capacitor C122 is connected to the node ND122,and a second electrode is connected to the power supply potential lineVCCL102 arranged at the second column. The source of the TFT 124 isconnected to the node ND122, the drain is connected to the signal lineSGL102 arranged at the second column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT125 is connected to the node ND121 (gate of the TFT 121), and the drainis connected to the precharge potential line VPCL102 arranged at thesecond column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second column ofthe second row of FIG. 19, the source of the TFT 121 used as the drivetransistor is connected to the node ND123 (connection point of thesource of the TFT 122 and the drain of the TFT 123), the drain isconnected to the anode side of the organic EL element 126, and thecathode of the light emitting element 126 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 122 is connected to the node ND123(source of the TFT 121), the drain is connected to the power supplypotential line VCCL102 arranged at the second column, and the gate isconnected to the drive line DRL102 arranged at the second row. The drainof the TFT 123 is connected to the node ND123 (source of the TFT 121),the source is connected to the node ND122 (source of the TFT 124), andthe gate is connected to the auto zero line AZL102 arranged at thesecond row. A first electrode of the capacitor C121 is connected to thenode ND121, and a second electrode is connected to the node ND122.Further, a first electrode of the capacitor C122 is connected to thenode ND122, and a second electrode is connected to the power supplypotential line VCCL102 arranged at the second column. The source of theTFT 124 is connected to the node ND122, the drain is connected to thesignal line SGL102 arranged at the second column, and the gate isconnected to the scanning line SCNL102 arranged at the second row. Thesource of the TFT 125 is connected to the node ND121 (gate of the TFT121), and the drain is connected to the precharge potential line VPCL102arranged at the second column.

The operation of the pixel circuit 101E is basically the same as that ofthe circuit of FIG. 13, so a detailed explanation is omitted here.

Further, the timings of the offset cancellation will be considered. Inthe sixth embodiment as well, the precharge potential lines VPCL arearranged parallel to the signal lines SGL. At this time, the number ofpixels connected to one of the precharge potential lines VPCL parallelto the signal lines SGL and simultaneously offset cancelled is K.Usually, K is the offset cancellation period and the time necessary forthe sufficient offset. It is usually 1 to several tens or less and smallin comparison with the number of pixels simultaneously offset cancelledin the related art. Further, even when the resolution of the panelrises, K does not change. Accordingly, it becomes easy to hold theprecharge potential at a stable potential.

According to the sixth embodiment, there are the effects the same asthose by the fifth embodiment mentioned above, that is, it is possibleto stably and correctly supply a current of the desired value to thelight emitting element of each pixel without regard to variation of thethreshold value of the active elements inside the pixels, it is possibleto stably hold the reference potential even when there is an offsetcancellation function by the precharge potential line, and it ispossible to prevent a gradient from being formed in the luminance of thedisplayed image. As a result, there is the advantage that a high qualityimage is able to be displayed.

Further, in the sixth embodiment as well, the power supply potentiallines VCCL are made common at the top and bottom of the display regionconstituted by the pixel array 102E in the figure, that is, the two endsof the plurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Therefore, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring between the top and bottom of the powersupply potential lines VCCL in the figure.

Note that the pixel circuit 101E of FIG. 19 is an example, and thepresent embodiment is not limited to this. For example, as mentionedabove, the TFT 122 to TFT 125 are only switches, therefore it is clearthat it is also possible to configure all or part of them by p-channelTFTs or other switch elements.

Seventh Embodiment

FIG. 20 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to a seventh embodiment of the presentinvention.

The difference of the organic EL display 100F according to the seventhembodiment from the organic EL display 100C according to the fourthembodiment resides in that a non-mirror type circuit arrangement isprovided. The rest of the configuration of the organic EL display 100Fis the same as that of the fourth embodiment, so the same components ofFIG. 20 as in FIG. 15 are represented by the same notations.

Each pixel circuit 101F according to the seventh embodiment has, asshown in FIG. 20, n-channel TFT 131 to TFT 135, capacitors C131 andC132, a light emitting element 136 made of an organic EL element OLED(electrooptic element), and nodes ND131 to ND133. Among thesecomponents, the TFT 131 forms the field effect transistor, TFT 132 formsthe first switch, TFT 133 forms the second switch, TFT 135 forms thethird switch, and TFT 134 forms the fourth switch. Further, the scanningline SCNL corresponds to the first control line. Note that, the autozero line AZL is commonly used as the control line for turning ON or OFFthe TFT 135, but it is also possible to perform the ON/OFF control byusing another control line. Further, the supply line (power supplypotential) of the power voltage V_(cc) corresponds to the firstreference potential, and the potential of the cathode line CSL (forexample the ground potential GND) corresponds to the second referencepotential.

Note that, in the pixel array 102F, pixel circuits 101F are arranged inan m×n matrix, but in FIG. 20, an example of arranging them in a 2(=m)×2 (=n) matrix is shown for simplification of the drawing. Further,in FIG. 20, the 2×2 pixel circuits are also labeled as “Pixel (M,N)”,“Pixel (M,N+1)”, “Pixel (M+1,N)”, and “Pixel (M+1,N+1)”.

Next, an explanation will be given of the specific configuration of eachpixel circuit 101F.

In the pixel circuit “Pixel (M,N)” arranged at the first row and firstcolumn of FIG. 20, the drain of the TFT 131 used as the drive transistoris connected to the power supply potential line VCCL101 arranged at thefirst column, the source is connected to the node ND133, and the gate isconnected to the node ND131. The drain of the TFT 132 is connected tothe node ND133 (source of the TFT 131), the source is connected to theanode side of the organic EL element 136, the gate is connected to thedrive line DRL101 arranged at the first row, and the cathode of thelight emitting element 136 is connected to the cathode line CSL of apredetermined potential (for example, the ground potential). The sourceof the TFT 133 is connected to the node ND133 (source of the TFT 131),the drain is connected to the node ND132 (source of the TFT 134), andthe gate is connected to the auto zero line AZL101 arranged at the firstrow. A first electrode of the capacitor C101 is connected to the nodeND131, and a second electrode is connected to the node ND132. Further, afirst electrode of the capacitor C132 is connected to the node ND132,and a second electrode is connected to the power supply potential lineVCCL101 arranged at the first column. The source of the TFT 134 isconnected to the node ND132, the drain is connected to the signal lineSGL101 arranged at the first column, and the gate is connected to thescanning line SCNL101 arranged at the first row. The source of the TFT135 is connected to the node ND131, and the drain is connected to theprecharge potential line VPCL101 arranged at the first column.

In the pixel circuit “Pixel (M+1,N)” arranged at the second row andfirst column of FIG. 20, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL101arranged at the first column, the source is connected to the node ND133,and the gate is connected to the node ND131. The drain of the TFT 132 isconnected to the node ND133 (source of the TFT 131), the source isconnected to the anode side of the organic EL element 136, the gate isconnected to the drive line DRL102 arranged at the second row, and thecathode of the light emitting element 136 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL102 arranged at the second row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL101 arranged at the first column. Thesource of the TFT 134 is connected to the node ND131, the drain isconnected to the signal line SGL101 arranged at the first column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 135 is connected to the node ND131,and the drain is connected to the precharge potential line VPCL101arranged at the first column.

In the pixel circuit “Pixel (M,N+1)” arranged at the first row andsecond column of FIG. 20, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL102arranged at the second column, the source is connected to the nodeND133, and the gate is connected to the node ND131. The drain of the TFT132 is connected to the node ND133 (source of the TFT 131), the sourceis connected to the anode side of the organic EL element 136, the gateis connected to the drive line DRL101 arranged at the first row, and thecathode of the light emitting element 136 is connected to the cathodeline CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL101 arranged at the first row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL102 arranged at the second column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL101 arranged at the firstrow. The source of the TFT 135 is connected to the node ND131, and thedrain is connected to the precharge potential line VPCL102 arranged atthe second column.

In the pixel circuit “Pixel (M+1,N+1)” arranged at the second row andsecond column of FIG. 20, the drain of the TFT 131 used as the drivetransistor is connected to the power supply potential line VCCL102arranged at the second column, the source is connected to the nodeND133, and the gate is connected to the node ND131. The drain of the TFT132 is connected to the node ND133 (source of the TFT 131), the sourceis connected to the anode side of the organic EL element 136, the gateis connected to the drive line DRL102 arranged at the second row, andthe cathode of the light emitting element 136 is connected to thecathode line CSL of a predetermined potential (for example, the groundpotential). The source of the TFT 133 is connected to the node ND133(source of the TFT 131), the drain is connected to the node ND132(source of the TFT 134), and the gate is connected to the auto zero lineAZL102 arranged at the second row. A first electrode of the capacitorC131 is connected to the node ND131, and a second electrode is connectedto the node ND132. Further, a first electrode of the capacitor C132 isconnected to the node ND132, and a second electrode is connected to thepower supply potential line VCCL102 arranged at the second column. Thesource of the TFT 134 is connected to the node ND132, the drain isconnected to the signal line SGL102 arranged at the second column, andthe gate is connected to the scanning line SCNL102 arranged at thesecond row. The source of the TFT 135 is connected to the node ND131,and the drain is connected to the precharge potential line VPCL102arranged at the second column.

The biggest difference between the pixel circuit 101F of FIG. 20 and thepixel circuit 101E of FIG. 19 resides in that the TFT 131 used as thedrive transistor for controlling the current flowing in the lightemitting element (OLED) 136 is the n-channel, and the source thereof andthe organic EL element (OLED) are connected via the TFT 132 as theswitch.

The operation of the pixel circuit 101F is basically the same as that ofthe circuit of FIG. 15, so a detailed explanation thereof is omittedhere.

According to the seventh embodiment, there are the effects the same asthose by the fifth and sixth embodiments mentioned above, that is, it ispossible to stably and correctly supply a current of the desired valueto the light emitting element of each pixel without regard to thevariation of the threshold value of the active elements inside thepixels, it is possible to stably hold the reference potential even whenthere is an offset cancellation function by the precharge potentialline, and it is possible to prevent a gradient from being formed in theluminance of the displayed image. As a result, there is the advantagethat high quality image is able to be displayed.

Further, in the seventh embodiment as well, the power supply potentiallines VCCL are made common at the top and bottom of the display regionconstituted by the pixel array 102F in the figure, that is, the two endsof the plurality of power supply potential lines VCCL101 to VCCL10 n areconnected in common to make the potentials the same. Therefore, it ispossible to prevent uneven luminance due to the potential difference inthe length direction occurring between the top and bottom of the powersupply potential lines VCCL in the figure.

Note that the pixel circuit 101F of FIG. 20 is an example, and thepresent embodiment is not limited to this. For example, as mentionedabove, the TFT 132 to TFT 135 are only switches, therefore it is clearthat it is also possible to configure all or part of them by p-channelTFTs or other switch elements.

Eighth Embodiment

FIG. 21 is a circuit diagram of an active matrix type organic EL displaydevice (display device) according to an eighth embodiment of the presentinvention. Further, FIG. 22 is a diagram of the layout of the powersupply lines of the active matrix type organic EL display deviceaccording to the eighth embodiment.

The difference of the eighth embodiment from the above sixth embodimentresides in the point that the precharge potential lines VPCL are sharedbetween two pixels adjacent in the scanning line direction. Due to this,it is possible to halve the number of precharge potential lines VPCLarranged in the signal line direction.

Further, it is also able to share the precharge lines of L pixelsadjacent in the direction parallel to the scanning lines. In this case,the number of pixels connected to one of the precharge lines parallel tothe signal lines and simultaneously offset cancelled is K×L. At thistime, it is also possible if a suitable numerical value is selectedwithin a range where the precharge line is able to be held at the stablepotential as L.

As explained above, according to the present embodiment, it is possibleto prevent crosstalk between pixels with a relatively simple layout.Further, it is possible to prevent the occurrence of uneven luminance inthe displayed image, it is possible to stably and correctly supply acurrent of the desired value to the light emitting element of each pixelwithout regard to variation of the threshold value of the activeelements inside pixels, and as a result it is possible to display a highquality image.

Further, according to the present embodiment, it is possible to stablyand correctly supply a current of the desired value to the lightemitting element of each pixel without regard to variation of thethreshold value of the active elements inside the pixels, it is possibleto stably hold the reference potential even when there is an offsetcancellation function by the precharge potential line, it is possible toprevent a gradient from being formed in the luminance of the displayedimage, and as a result of this it is possible to display a high qualityimage. Namely, without using a three-dimensional electromagnetic shield,it is possible to prevent crosstalk between pixels with a relativelysimple layout of adding a single fixed potential line on a plane.Further, various variations can be applied as the fixed potential line.Further, there is the advantage that the uneven luminance does not occurbetween the top and bottom of the screen.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What we claim is:
 1. A display device comprising: a plurality of pixelcircuits arranged in a matrix, the matrix including first, second andthird columns respectively including columns of the pixel circuitsextending along a column direction; signal lines for supplying datasignals; precharge potential lines arranged in the column direction;power supply potential lines arranged in the column direction, whereinone of the power supply potential lines is shared by pixel circuits inthe first and second columns, wherein one of the precharge potentiallines is shared by pixel circuits in the second and third columns,wherein the second column is adjacent to the first column, the secondcolumn is adjacent to the third column, and the second column is betweenthe first column and the third column, wherein the one of the powersupply potential lines is located between the first column and thesecond column, but none of the precharge potential lines are locatedbetween the first column and the second column, wherein the one of theprecharge potential lines is located between the second column and thethird column, but none of the power supply potential lines are locatedbetween the second column and the third column, and wherein transistorsof a first pixel circuit in the first column and transistors of a secondpixel circuit in the second column are arranged in a symmetrical mannerwith respect to an axis along the column direction.